Journal of Wood Chemistry and Technology

Over the past few years, research activities aimed at increasingthe utility of one of our most important natural resources, wood,have grown enormously. Yet existing journals have not been whollysuccessful at keeping pace with new developments, with the result thatthat scientists in need of a key journal that highlights major new con-tributions have, instead, had to cope with a plethora of tangentialsources.

Focusing exclusively on the chemistry of wood, wood compo-nents, and wood products, the Journal of Wood Chemistry and Tech-nology fills this need of researchers by presenting comprehensive, up-to-date coverage of investigations that add new understanding tochemical phenomena important to wood technology. In each issue,some of the most active and innovative researchers in their respectivespecialties present their latest work on such topics as new approachesand insights into the chemistry of pulping; lignin, cellulose, hemicel-lulose, and extractives chemistry; chemicals derived from wood andbark and their isolation; wood bonding; and biomass conversion andutilization. Reviewed by an editorial board composed of internation-ally renowned researchers in the field, the articles in the Journal ofWood Chemistry and Technology are of great value to wood chem-ists, cellulose and lignin chemists, chemical engineers, wood technolo-gists, research scientists and engineers, process engineers, physicalchemists, and biologists.

With its complete coverage and its rapid lab-to-print foTDlat, theJournal of Wood Chemistry and Technology presents scientists witha sharply focused, eminently useful source of pra~tica1, infoTDlativematerial that is of great value to a wide range of research and appliedendeavors.

JOURNAL OF WOOD CHEMISTRY AND TECHNOLOGY, 5(1), 135.-158 Q985}

CONDENSED TANNINS: REACTIONS OF MODEL COMPOUNDSWITH FURFURYL ALCOHOL AND FURFURALDE8YDE

L. Yeap FooChemistry Division

Department of Scientific and Industrial ResearchPetone. New Zealand

Richard W. HemingwaySouthern Forest Experiment Station

2500 Shreveport HighwayPineville. Louisiana 71360

ABSTlAC'r

Reaction products of phloroglucinol or catechin withfurfuryl alcohol and furfuraldehyde were studied. Inreactions of furfuryl alcohol with phloroglucinol. only2-furyl-(1'.3'.5'-trihydroxyphenyl) methane was obtainedas product. and 53% of the phloroglucinol was recovered.Reactions of furfuryl alcohol with catechin gave 2-furyl-(8-catechinyl) methane and 2-furyl-(6-catechinyl) methanein 4.0% and 1.5% yields.. respectively. while 62% of thecatechin was unreacted. Polymeric furans with few catechinmoieties made up the oligomeric products (38% of catechin).Reaction of phloroglucinol with furfuraldehyde gave 2-furyl-di(1'.3'.5'-trihydroxyphenyl) methane. an unstable productthat readily polymerized during isolation. The solid statel3C-NMR spectrum of the higher polymers suggested onephloroglucinol moiety per luran unit. but lower oligomerscontained more furan-furan condensation products. Reactionsof catechin with furfuraldehyde gave 2-furyl-di(8-cate-chinyl) methane and the two diastereomers of 2-furyl-(6-catechinyl)-(8-catechinyl) methane in low yield. with 65%of the catechin unreacted.

135

0277-3813/85/0501-0135 $3 .s0/0

136 FOO AND HEMINGWAY

INTRODUCTION

Rapid development of new composite wood products has

placed the forest products industry in a position of heavy

reliance on chemical manufacturers for adhesives. The petro-

leum shortage of the mid-1970's. in juxtaposition with a strong

housing demand. caused the forest products industry to intensify

the search for alternative adhesives based on their own resources.

such as lignins. tannins. and furaos. Reportsl-3 on the use of

condensed tannin-furan systems as wood adhesives have suggested

that the combination of these two renewable resources may hold

promise as an approach that would permit the forest products

industry to be more self-sufficient.

The apparent advantages of replacing formaldehyde with

furfuraldehyde in tannin-based adhesives could include more

controllable condensation reactions because of possible steric

constraints and also could afford an opportunity to overcome

possible health concerns associated with the use of formaldehyde.

Both furfuryl alcohol and furfuraldehyde undergo self condensation

in the presence of acid catalysts to give polymers primarily of

types (1)4-6 and (!)7. respectively. In view of the facile

~0

Oat2 ii:). CH2 q CH2 OH 1i"""\\--1~a«)0

OHC A_r -0 M

(1)(2)

self-condensation reactions of these compounds, there is

question about the degree of intermolecular tannin-furan chemi-

cal bonding required to produce copolymers in adhesive appli-

cations. In addition, suitable model compounds, necessary for

1'1CONDENSED TANNINS

interpretation of the structure and properties of the polymers,

h.ve not been described. This study was undertaken to make

appropriate model compounds and to gain more information about

how readily furfuryl alcohol and furfuraldehyde react with

flavanoids bearing a phloroglucinol A-ring representative of the

condensed tannins from conifer barks.

BESULTS ~_D _DISCUSSION

Reactions With Furfuryl Alcohol

The phloroglucinol ~-ring in catechin <1) bas been demon-

strated to readily undergo electrophilic substitution.8,9

OH

iotoHO

OH

(3)

where R - Br

- ~ or -~-hydroxybenzyl

- 4-flavanyl

The ready acid-catalyzed condensation of furfuryl alcohol

probably proceeds via a carbocation intermediate, so it may

be captured by the phloroglucinol !.-ring of the flavanoid unit.

When phloroglucinol was reacted with furfuryl alcohol in

alcohol solution with an acetic acid catalyst, little or no

phenol reacted. Both hydrochloric and ~-toluene sulfonic acids

were used in attempts to force the condensation, but this only

resulted in rapid resinification of the furfuryl alcohol. To

promote intermolecular condensation and to minimize furan self-

138 FOO AND HmIINGWAY

condensation, aqueous solutions of phloroglucinol and furfuryl

alcohol ~ere treated at lOOOC in the presence of acetic acid.

These conditions provided a phloroglucinol reaction product in

lCN yield (10%) together with some oligomeric .terials.. The

phloroglucinol derivative was shCNn to be 2-furyl-(l',3',5'-

trihydroxyphenyl)-methane (~) from 13c-and lH-NMR data (Tables

land 2). Both the phloroclucinol and furan rings were clearly

discernible, with the .ethylene protons appearing at 6 3.90 PPM

and the carbon chemical 8hift at 21.6 PPM. Acetylation of this

product gave the triacetate as colorless crystals whose 13c-

and IH-NMR spectra were fully consistent with the propo8ed

structure (~).

"4 '5 HO ~OM

F"\2 /~4'"0/'C"2 OM

(.1)

Attempts to make the di- and tri-8ubstituted phloroglucinol

derivatives through use of a higher IOOlar ratio of furfuryl

alcohol to phloroglucinol only resulted in a decrease in yield

of product <i) and an increase in yield of oligomers.

Considerable unreacted phloroglucinol vas recovered from these

reactions, suggesting that these oligomers were predoainantly

polymeric furans.

When catechin vas used in place of phloroglucinol, two

low molecular weight phenolic products were obtained and purified

by reverse-phase HPLC. l3C-NMR data of these products clearly

showed that bothvere made up of equimolar proportions of catechin

to furan units and were hence regioisomeric to one another.

Studies of proton chemical shifts of substituted catechin deri-

vatives by Hundt and RouxlO and by Batterham and Highetll have

established that, in flavanoid systems, the H-8 chemical shift

~a

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141CONDENSED TANNINS

occurs at lower field than does the corresponding B-6 signal.

Examination of the lB-HMR of the two compounds showed that the

more mobile compound had a phloroglucinol A-ring proton at

~ 6.03 PPM and that the other compound had an A-ring at ~ 6.13 PPK

On this basis, the more mobile compound was assigned structure (1)

with substitution at C-8, and the other compound was assigned

structure (~) of the C-6 substituted isomer. The assignments of

~

00

(~(1)

structures of these compounds were further corroborated h, the

IH-NMR data of the penta-acetate derivatives. Though there was

little difference in the chemical shifts of the A-ring protons,

the methylene bridge protons differed h, 0.18 PPM with the C-6

substituted isomer more downfield than the C-8 substituted

derivative. Similar differences in the chemical shifts of

methylene bridge protons were obaerved in the peracetates of

~- and ~-hydroxybenzyl substituted catechin.8 The larger down-

field shift of the C-6 substituted peracetates was probably caUSE

by the exposure of the methylene protons to the deshielding regic

of the two neighboring acetate functions, whereas only one acetal

at C-7 was adjacent to the methylene protons in the C-8 substitul

derivative.The yields of the two isomers were low, about 4.0% for the

C-8 substituted product and 1.5% for the C-6 substituted isomers

The ratio of yields of 2.7:1 for the C-8 to C-6 isOiler reflects

the greater reactivity at the C-8 position,which is in

142 FOO AND HFJfINGWAY

t " th " b " d " " 812agreemen WI rKlOS 0 talne l.n other studIes.' Unreacted

catechin was recovered in about a 62% yield. while oligomeric

materials accounted for about 38% of the catechin. Most of the

latter llaterial precipitated out of the aqueous reaction mixture

as a gum~ solid. The yield of the precipitate increased

from 38% after 2.5 hours of heating to about 49% after 4.5

hours. A s~le of these oligomeric products was fractionated

on Sephadex LR 2013 using ethanol as the solvent. Tbe low

molecular weight products and unreacted starting materials were

eluted in the first fractions. and the oligomeric products were

separated into more (.!) and less ~bile (.!) fractions.

Small samples of each fraction were acetylated. and the number

average molecular weights were determined by vapor pressure

osmometry. both for the parent and acetylated derivatives (Table

3). The separation obtained on the Sephadex column was a

function of molecular weight. the more mobile fraction being of

lower molecular weight. The carbon and hydrogen analyses of

the two fractions and of their peracetate derivatives were

nearly identical. suggesting very similar compositions.

However. the larger change in molecular weight obtained by

acetylation of the higher molecular weight fraction suggests

a higher proportion of catechin moieties in these oligomers than

in the less condensed fractions. an observation counter to that

which would be expected from a simple linear polymer structure.

Evidence for the presence of catechin functionality in the

oligo_rs was obtained from their 13C-NMR .spectra. 14 Prominent

signals observed at chemical shifts of 67.8 and 81.8 PPM were

attributable to the C-3 and C-2. respectively. of the catechin

heterocyclic ring.. Also apparent were signals consistent with

the furan ring and the !Ethylene bridge carbon at 22.0 Pftf.

The location and shape of the furan signals were in many

respects similar to those observed in a homogeneous furan

polymer obtained by heating furfuryl alcohol alone in aqueous

CONDENSE!) TANNINS .-43

TABLE 3

Molecular Weight and Compo8ition of Oligomer8 fromReaction of Catechin with Furfuryl Alcohol

Mwn ~- %It

1096

1232

1679

2170

63.9

62.8

64.3

63.1

5.3

5.05.35.0

Sample A

Peracetate of A

Sallple B

Peracetate of.

solution with an acetic acid catalyst. The broad signal at 107

PPH is assigned to the C-3 and C-4 of the furan unit, with di-

substitution at the C-2 andC-5 po8itions.l5 Though a large

proportion of intermolecular linkage8 are between furan unit8

themselves, it i8 clear that there are 8ome bonds between fur an

and catechin units in these oligO8er8.

Reactions With Furfuraldehyde

Unlike reactions with furfuryl alcohol, acetic acid

readily catalyzes the condensation of furfura1dehyde with the

formation of black glassy products in alcohol solutions heated

at 100OC. The reactions of furfura1dehyde with phloroglucinol

and catechin were .ore controllable when carried out at ambient

temperature. Formation of excess polymeric products could be

avoided by restricting the reaction time to several hours and

stopping the reaction as soon as the gummy precipitate

appears. Overnight reactions at ambient temperature gave

mostly insoluble polymers.

In the reaction of furfura1dehyde with phloroglucinol, only

one low 8)lecu1ar weight product was obtained. The 13c-RMR

spectra clearly showed furan carbon chemical shifts at 105.9,

110.0, and 141.0 PPH, together with the quarternary carbon at

154.9 PPM (Table 4). The phloroglucinol carbon shifts occurred

144

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U'\

1 ...

1{I)

~S0~...f~&(;11II,,,,,11I...

~I.

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,...1

N

co-. --

1 .

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-d'\D

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00 -- -

N

NN

NM

.:-.;

~

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1,......~

I""

1C

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'4 .~I"I~. .,...,...-0-0

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O

AN

D

HE

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GW

AY

0do~dU

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CONDENSED TANNINS 145

at 106.5 PPM for the 8ubetituted carbon and at 96.3 PPH for the

un8ubstituted carbone. The bridging methine carbon signal was at

30.3 PPH. On the basis of the IJc-NKR spectrum. the product

could be assigned structure (L). this structure could a180 be

confirmed by the lR-RMR data (Table 5). The phloroglucinol ring

protons occurred at 6 6.05 PPH. Also. the signal at ~ 7.30 PPH ie

attributable to the furan R-5.and the 811tiplet8 that integrated

for two protons at ~ 6.25 PPM account for the R-3 and H-4 protons.

- .

(D.,

Although product (L) vas rea~ily separated from starting

materials and oligomera by chromatography on Sephadex LH-20.

cellulose TLC of the freeze-dried products invariably showed

the presence of phloroglucinol and oligomers as impurities. even

after repeated chromatography and drying. The TLC of the

eluate from the Sephadex column shoved that complete separation

had been achieved. Thes~ observations suggest that product

(L) is unstable and possibly undergoes self-condensation to

oligomera (i.e.. !) with the release of phloroglucinol. A sample

of the purified compound (L) when heated in water or alcohol

gave high yields of phloroglucinol and oligomers. Additionally.

product (L) also decomposed after standing for several days in

ethyl acetate at ambient temperature. In comparison. 2-furyl-

(1'.3'.5'-trihydroxyphenyl) -thane (i) is stable. so the .thine

U'\

M~~ 146"i..c"'0...:s~..~.c~..4.~0..4~U.".~0e~u:s'00..~..0~e~~'"~.U..4m6~I='0"~<

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GI

~G

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I~~>

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...~

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~'0dge-oCo) .0=

....~:5c.~

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=

4J.~cc~

=c.~~r&

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iI,I,,,III~~~11-1

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N~

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COftDENSm TAIOfINS 147

carbon in <1) 8U8t be particularly reactive a8 a re8ult of the

extra phloroglucinol moiety attached to it. The ready 8ub8ti-

tution at thi8 bridging carbon may be cO8pared with the C-4 in

procyanidin8 Where two phloroglucinol !-ring8 are attached. The

interflavanoid bond of procyanidin8 i8 a180 labile. but much le88

so than <1). Steric barrier8 around the C-4 of the interflavanoid

bond in procyanidin8 may 8low thi8 reaction in compari80n to a

compound 8uch as <1.). Bowever. the in8tability of <1) i8 another

exa8ple of the reactivity of a .ethine carbon sub8tituted vith two

unit8 of phloroglucinol functionality. a8 occur8 in the conden8ed

tannin8 of 8O8t conifer bark8 in contra8t to the tannin8 of vattle

which con8ist of flavan unite vith re8orcinol !-ring8 and which art

con8iderably more 8table to cleava.e.16

When the reaction of phloroglucinol and furfuraldehyde vas

conducted in ethanol at higher solidi content, highly condensed

in80luble product8 were obtained. Only ...11 amount8 of

phloroglucinol were detected when the precipitate vae va8hed with

organic 80lvent8. The fact that pblorollucinol vae a major

constituent of the pol,.er va8 a180 shown by a 80lid 8tate 13c-KMR

8pectrum that was consistent with etructure <!). The chemical

8hift8 of the 80lid e..ple appeared approxi8ately 2 PPM downfield

from th08e of the eolution spectru. of <1.). The di8tinctive

methine carbon, which bridges the furan and phloroglucinol rings

ob8erved at 30.3 PPM in the 80lution 8peCtrua of <1). i8 at 32 PPt

in the 8pectrum of the 8olid sample. UDlike eolution 13c-MKR

eignals. the eolid probe provides chemical ehifts of comparable

intensity a8 a re8ult of close proxi.ity to a hydrog~n in the soli

state. Bence. to determine the ratio of the luran to the

phloroglucinol functionality. the relative area8 of the eignals al

154. 143. 109. and 99 PPM were .asured. eince the ooaber of fura!

moieties may not neceesarily be the same as the number of

phloroglucinol unit8. The signal at 143 PPM i8 attributable to

only C-5 of the furan ring. and the signal at 99 PPM is

14'6 FOO AND HEMINGWAY

attributable to only unsubstituted carbon of the phloroglucinol

ring. Since the areas of these two .ignals are approximately

equal. there is about one furan unit for every phloroglucinol unit

in the polymer. In the solution spectrum of furfuraldehyde. the

carbon R to the aldehyde group has a chemical shift of 123 PPH.

The solid state l3C spectrum of the insoluble polymer also has

signals at 124 and 126 PPH. indicating the presence of

furfuraldehyde self-condensation products. Further indications

of self-condensation of the furan are the distinctive signals at

14 and 17 PPM.which can be attriooted to --thyl carbons in --thyl

furan15 presumably brought about by disproportionation of the

aldehyde functionality.

Catechin shows less reactivity than phloroglucinol in

condensation reactions with furfuraldehyde. Unlike reactions with

phloroglucinol. catechin and furfuraldehyde did not react to form

a gel under conditions of high solids content. The cO8bined

yield of low molecular weight products was also smaller. and over

60% of the catechin was recovered after reaction.

In reactions of catechin with furfuraldehyde. substitution

occurred at both the C-6 and C-8 positions to give ri8e to

several regio-i8o~rs that were difficult to separate..

~

(.2)

However, the C-8, C-8 substituted product <2.> vas isolated by

repeated chroBlatography on Sephadex LH-20 by first eluting with

CONDENSED TANNINS 149

ethanol and then rechroaatography of the partially purified

product using ethanol_ater (.1:1, v/v) solvant. In both the

l3C- and lH-NMR spectra, signals attributable to catechin and

furan units were readily apparent, and the .thine carbon

appeared at 30.0 PPM, which is consistent with the bridging

carbon in (l) (Tables 4 and 5). The 13C-NMR spectrum showed the

substituted and unsubstituted carbons of the phloroglucinol

!-rings at chemical shifts of 106.6 and 96.6 PPM, which are

consistent with substitution at the C-8 positions of both

catechin units.16 It is interesting to note that the C-2 (82.1

and 82.4 PPH), C-3 (67.4 and 67.6 PPM), and the substituted C-8

(106.5 and 106.7 PPH) chemical shifts of the two catechin units

were not coincident, suggesting unusual phenomenon of intet:nal

att:opiso.ris18 arising ft:08 steric constraint to ft:ee rotation

about the interflavanoid bond.

Two other products of the t:eaction of catechin with fur-

furaldehyde were isolated by chromatography on Sephadex LR-20

and then separated further by HPLC on Zorbax CN coluans eluted

with methanol-water (15:85, v/v). The l3c-NKR data of both

compounds were in many respects similar to the spectrum of (!)

and almost identical to each other. The presence of two

sepat:ate chemical shifts at 95.8 and 97.0 PPM for the more

mobi Ie compound on HPLC and at 95.8 and 96.9 PPM for the other

c~ound that were attt:ibutable to unsubstituted C-8 and C-6

catechin A-ring carbons, t:espectively, clearly showed that the

two compounds must have two catechin units, one substituted at

the C-6 position and the othet: at the C-8 position.16 This

conclusion was also corroborated by the two distinct substituted

!-t:ing carbon signals at 106.4 and 107.4 PPH that were assigned

to the substituted ~-8 and C-6 cat:bons, respectively, in the more

mobile compound. Similar diffet:ences in the chemical shifts of

the substituted !-ring carbons were observed for the otbet:

compound at 106.4 and 107.4 PPM, respectively. These two

150 POD AND HEMINGWAY

compounds are therefore diastereomers. In the! and ~ convention,

the C-8 substituted catechin has priority over its C-6 substituted

counterpart, so the! iso_r is compound (lQ.) and the ~ iso_r 1s

compound (l!.). Although the IJc- and lH-NMR data clearly shCN

Co

~OH(~) (Jjjc

that the8e two compounds are C-6 and C-8 sub8tituted diastereomers,

assignment of the configuration of the two products has not yet

been possible. Efforts to resolve this question are continuing.

The C-6 and C-6 substituted isomer was not isolated. Difficulty in

obtaining this product was not unexpected, since other studies8,12

have shown that the C-6 position is only about one-third as

reactive as the C-8 position in substitutions with bulky electro-

philes.

The products of the reaction of catechin with fur-

furaldehyde, such as <!), are relatively stable in comparison

to the phloroglucinol derivative <1..). This is possibly

caused by the bulk of the catechin function inhibiting further

condensation, possibly through nucleophilic displacement

reactions such as that proposed for the formation of <!).

However, under acidic conditions and in the presence of

phloroglucinol or phenyl-aethane thiol as nucleophiles, product

<!) readily released catechin as in the acid-catalyzed cleavage

of the interflavanoid bond of procyanidins.16

'CONDENSED TANNINS 1$1

EXPERIMENTAL

lH-NKR spectra at 80 MHz and l3C-RMR spectra at 20 MHz

were recorded with a Varian FT-80A spectrometer.l3 High

performance liquid chromatography (HPLC) was carried out on aWaters Associates M-6000 liquid chro.atograph.l3 Two dimen-

sional thin-layer chromatography (TLC) was with Schleicher and

Schull F-1440l3 cellulose sheets in the solvent syste118 (A) t-

butanol-acetic acid-water (3:1:1, v/v/v) and (B) 6% acetic acid

(v/v). Plates were visualized after spraying with either

vanillin-HCl, ferric chloride-potassium ferricyanide on

cellulose, or formalin-H2SO4 on Si-gel plates. Column

chromatography was with Sephadex LH-2013 in columns 15 mm

or 25 mm (i.d.) x 900 mm long.

2-Furyl-(1'.3'.5'-tribydroxYphenyl) mtbane (i)

Phloroglucinol (3.2 g) and furfuryl alcohol (2.0 g)

were 8u8pended in water in the pre8ence of BOAc (1.0 ml) in a

8ealed vial and the mixture heated at 10SOC for 2 hour8. The

8o1uble reaction mixture was 8eparated froa the precipitated

gum and freeze-d~ied. The dried product was fractionated by

chromatography on Sephadex LH-20. u8ing EtOH-B20 (1:1. v/v) a8

the 8olvent. Fraction8 were monitored by cellulo8e TLC devel-

oped with 6% HOAc. The product was i8olated and freeze-dried

to give 0.43 g of a light-colored 8o1id. Rf (A). 0.80; Rf (B).

0.90. 1B-NMR in acetone-d6: 6 7.93 (br.OB); 7.25 (m,lB); 6.20

(m,lB); 6.00 (8,2B); 5.84 (m.lB); and 3.90 (28). 13c-HMR in

acetone-d6: 21.6, 95.0, 104.8. 107.3, 110.3, 140.3, and 157.2

PPH.

Acetylation with pyridine-acetic anhydride .ave the

triacetate. whi~h vas crystallized from EtO&-B20 as colorless

plates. m.p. 98-99OC. Found: C. 61.3; B. 4.9%; C17B1607

requires C. 61.4; B. 4.8%. IB-NMR in CDC13: ~ 7.23 (m.lB);

6.89 (s.28); 6.22 (m.lB); 5.86 <-.lB); 3.83 (bs.2ft); and 2.25.

152FOO AND HEMINGWAY

2.22 (9ft). 13C-MMR in CDC13: 20.7, 21.6, 23.4, 106.0, 110.2,

114.1, 120.5, 141.0, 152.0, and 168 PPM.

2-Furyl-(6-catechinYl) .thane (..6..)

Catechin (2..9 g) and furfuryl alcohol (1.0 g) were

dissolved in H2O (100 _1) containing HOAc (1.0 81) in a sealed

vial, and the mixture was heated at lOOoC for 2 hour8. The

80luble rea~tion mixture was separated from the precipitated

gum and freeze-dried. The product was fractionated by chroma-

tography on Sephadex LB-20 by eluting with EtOH-B20 (1:1, v/v)

as the 80lvent. Fractions (20 _1) were collected, and tubes

104-113 gave 0.10 g of crude product. The compound was

purified by HPLC on a DuPont Zorbax CN column (9.4 - x 25 cm)by eluting with MeOH-H20 (20:80, v/v) at a flow rate of 2.0

ml/min, where compound (..6..) was eluted at a retention of

33.0 ml. TWo dimensional cellulose TLC showed one compound at

Rf (A) 0.60 and Rf (B) 0.85. 1H-HHR in acetone-d6: ~ 7.80

(vb,OH); 7.21 (d,lH); 6.75-6.87 (3H); 6.15 (a,lH); 6.13 (8,lH);

5.80 {m,lH); 4.60 (m,lH); 3.85 (s,2H); and 2.6-2.9 (_,28).

13c-NKR in acetone-d6: 21.9, 28.6, 67.8,81.9, 95.4, 105.1,

107.5, 110.3, 140.6, and 155.0 PIIM. MS, m/e (I): 370 (55),

265 (30), 219 (100), 177 (50), and 152 (45).

Acetylation of compound (..6..) with acetic anhydride and

purification on TLC (Si-ge1, benzene-acetone 4:1, vlv, Rf 0.63)

gave the penta-acetate. Found: C, 61.9; H, 4.91; C3d12sO12 requires

C, 62.1; H, 4.8%. 1H-NKR in CDC13: ~ 7.1-7.3 (m,38); 7.12

(m,lH); 6.63 (s,lH); 6.24 (m,lH); 5.91 (a,lH); 5.1-5.2 (m,28);

3.93 (8,2H); 2.7-2.80 (m,2B); 1.99 (8,3H); and 2.26 (br s,l21). 1

13c ~ .d 23 4 68 4 78 0 06 ~-nnA 1.n acetone- 6: .2, 2 .8, " " 1 .1, 109.0, i";j~;,,~

110.5, 116.8, 141.4, and 152.0 PIIM. .,ji

2-Furyl-(S-catechinvl) Ethane (~)

Further elution of the Sephadex LH-20 colusa with the ,-

solvent gave the crude product in fractions 122-140 (160 ~).

OONDENSED TANNINS JS3

A sample was purified by BPLC on a DuPont Zorbax CN column

under the conditions above to obtain compound (1.) at a retention

volume of 27.0 m1. Two dimensional cellulose TLC 8bowed one

cOq>ound at Rf (A) 0.65 and Rf (B) 0.55. IB-NMR in acetone-d6:

6 7.75 (vb,OB); 7.25 (m,lB); 6.50-6.85 <_,3B); 6.15 (m,lB);

6.03 (s,lB); 5.85 (_,lB); 4.55 (m,lB); 3.90 (br s,2B); and

2.6-2.9 (_,28). 1Jc-NMR in acetone-d6: 21.9, 28.4, 68.1, 82.3,

95.7, 105.1, 107.5, 110.4, 140.4, and 154.2 PPM. MS, mle (%):

370 (10O), 219 (80), 218 (70), 251 (7O), and 123 (75).

Acetylation of co~ound (2) with pyridine-acetic anhydride

gave the penta-acetate tbat was purified on TLC (Si-ge1, benzene-

acetone, 4:1, vlv, Rf 0.65). Found: C, 61.9; B, 4.9%; C3oB2sO12

requires C, 62.1; B, 4.8%. 1B-NMR in CDC13: ~ 7.21-7.31 (-,3D);

7.19 (br s,lB); 6.69 (s,lB); 6.23 (m,lB); 5.90 (_,lB); 5.0-5.2

(_,28); 3.75 (s,2B); 2.6-2.83 (m,2B); 2.26, 2.23 (12B); and 1.97

(8,3B). 13c-NMR in acetone-d6: 22.5, 24.3, 68.3, 78.0, 105.9,

109.9, 110.5, 116.2, 141.2, and 152.6 PPM.

2-Fury1-di(1'.3'.S'-trihydroxypheny1) ~thane (1)

A mixture of phloroglucinol (6.5 g) and furfura1dehyde

(2.0 g). water (100 ml) containing St~R (10.081). and acetic

acid (1.0 .1) was stirred for 4.5 hours at aabient temperature.

The resulting dark green suspension was filtered over glass-

wool. and the filtrate was freeze-dried. The dried product was

chromatographed on Sephadex LR-20. using StOR-R20 (1:1. v/v) as

the solvent. Phloroglucinol was recovered in tubes 18-30. and ~

crude isolate of the product was recovered in tubes 64-106.

Oligomeric products were collected in tubes 130 and up. The

crude product was rechromatographed on Sephadex LR-20. using

the same solvent system to remove further quantities of phloro-

glucinol and oligomers. Although cellulose TLC of the eluate

in tubes 64-106 showed only one product. after freeze-drying

and sample work-up the cellulose plates showed phloroglucinol

and oligomeric impurities. A sample of co8parative1y pure co.-

154 FOO AIm BEHIHGWA Y

pound vas finally obtained in which the cellulose TLC showed.

one predominate spot at af (A) 0.68 and af (B) 0.80. lR-RMR in

acetone-d6: A 8.2-8.8 (br.OB); 7.30 (br a.lB); 6.25 (8.28);

6.05 (s.48); and 5.98 (a.lR). 13c-RKR in acetone-d6: 30.3.

96.3. 105.9. 106.5. 110.0. 141.0. and 154.9 PPH.

Acetylation of (1.) with pyridine-acetic anhJdride gave the

hexa-acetate. Which vas purified by preparative TLC (Si-gel.

benaene-acetone. 4:1. v/v. If 0.55). Cryatallization fro. MeOB

gave colorle.s platea. ..p. 184OC. Found: C. 59.6; B. 4.7%.

C29B26013 requires C. 59.8. B. 4.5%. IH-RMI. in CDC13: ~ 7.28

(br a.lB); 6.86 (a.48); 6.22 (8.1B). 5.89 (a.lB); 5.83 (br

..IB); and 2.24. 1.97 (8.188). 13c-RKR in acetone-d6: 33.4. 107.9.

110.2. 114.5. 121.6. and 142.0 PPH; the quarternary carbon aignal

.u obscured.

Phloroglucinol-furfuraldehyde pol~rs (!)

Furfuraldehyde (10.0 g) and ROAc (3.0 al) were added to a

.olution of phloroglucinol (10.0 g) in EtOB (100.1). and the

aixture va. allowed to .tand at aabient t.-perature overnight.

The hard. dark-colored solid product wa. broken up and

thoroughly washed with EtOAc. acetone. and finally EtOB. The

washings contained only ...11 .-ounts of phloroglucinol. The

.olid residue was dried under vacuum for two day. and sent to

Dr. R. R. Rev8an. Che8istry Division. Depart.ent of Scientific

and Industrial Research. Petone. Rew Zealand. who recorded the

solid state l3C-KMR spectru. on an XL-200. The .pectru8 .howed

strong re.onance at 109 PPM assignable to C-3 and C-4 of the

furan unit and the substituted carbon of the phloroglucinol unit.

Another .trong sianal at 154 PPM vas a..igned to the quarternary

carbon of the luran unit and the hydro~lated carbons of the

phloroglucinol unit. The .ethine bridge carbon. vere apparent at

32 PPM. and less intense signal. were apparent at 99 PPM of the

unsubstituted phloroglucinol rina and at 143 PPM of C-5 ol the

furan unit. 88811 .ianal. were also ob.erved at 124 and 127 PPM.

155CONDENSFl> TANNINS

which were assigned to the C-2 carbon of the furan unit in which

an aldehyde function was retained, and at 14 and 17 PPM, which

were assigned to a methyl carbon that may have been obtained from

a disproportionation of the furfura1dehyde.

2-Furyl-di(8-catecbinyl) mtbane (!.)

Furfuraldebyde (6.7 g) and ROAc (1.081) were added to a

solution of catechin (10.0 g) in EtOH (100 al). and the mixture

was allowed to stand at ambient temperature overnight. The

reaction mixture was concentrated on a rotary evaporator at low

temperature. and the residue was diluted with H2O. This product

was freeze-dried and then fractionated by chromatography on

Sepbadex LH-20 with EtaH solvent by collecting l5.u fractions.

Unreacted catechin (7.0 g) was recovered in tubes 22-37. Crude

products were obtained from fractions 38-58 (1.0 g) and from

59-84 (0.45 g). Fractions 38-58 were combined and recbroma-

tograpbed on Sepbadex LH-20 eluting with EtOH-H20 (1:1. v/v).

As before. 15-.1 fractions were collected. and fractions 29-35

gave nearly pure compound (!.) in a yield of 175 mg. A small

sample of this product was purified further by HPLC (DuPont

Zorbax CR. 9.4 am x 24 cm. NeOR-H20. 15:85. v/v) to obtain the

product 4t a retention volu~ of 22.2 ml at a flCN rate of 2.0

ml/min. Two dimensional cellulose TLC showed one compound at af

(A) ().70 and af (B) 0.70. Found: C. 59.4; H. 5.1%; C3sH3c;J13.3H20requires C. 59.0; H. 5.1%. lH-NMR in acetone-d6: 6 7.6-8.2

(br.OH); 7.23 (-.lH); 6.5-6.8 (m.6H); 6.30 (s.lH); 6.06 (s.lH);

6.03 (..lH); 5.70 (-.iH); 4.59 (d.J-8Hz.lH); 4.32 (d.J-8Hz.lR);

3.7-4.1 (-.28); and 2.3-3.0 (-.4R). l3c-KKR in acetone-d6: 27.8.

30.0. 67.4. 67.6. 82.1. 82.4. 96.6. 105.4. 106.5. 106.7. 110.0.

140.8. and 156.3 PPK.

Acetylation with pyridine-acetic anhydride and preparative

TLC (Si-gel. benzene acetone. 4:1. vIvo at 0.43) gave the deca-

acetate. Found: C. 61.0; H. 4.8%; C55R50023 require8 C. 61.2;

H.4.6%. lH-RHR in CDC13: 6 6.7-7.2 (-.78); 6.50 (8.lR); 6.48

1.56 FOO AND HEKlNGWA Y

(s.lB); 6.20 (m.1B); 6.02 (s.lB); 5.80 (-.lB); 4.75-5.1 (-.2B);

4.70 (d.J=8Hz.18); 4.30 (d.J-8Hz.lB ); 2.2-3.1 (a.4B); and

1.7.-2.3 (m.3OR).2-Furyl-(6-catechiny1)-(8-catechinyl) !Ethane (A)

Continued elution of the above Sephadex L8-20 column with

EtOB-B20 (1:1. v/v) to fractions 54-68 gave a mxture of two

2-fury1-di-catechinyl methanes. These two compounds were

separated by BPLC (DuPont Zorbax CN. 9.4 mm x 25 ca. HeOB-B20.

15:85. v/v. 2 m1/min) to give the product A at a retention

volume of 26.5 m1. After preparative BPLC ~he product appeared

as primarily one compound on cellulose TLC Rf (A) 0.60. Rf (B)

0.75. Found: C. 58.0; B. 5.0%; C35B300l3.4H20 requires C. 57.5;

B. 5.20%. lB-NMR in acetone-d6: ~ 7.5-8.3 (br.OB); 7.27 (m.1B);6.7-6.9 (m.6B); 6.19 (s.lB); 6.10 (a.1B); 6.05 (s.lB); 5.94

(m.1B); 5.90 (-.18); 4.58 (d.J-8Bz.lB); 4.55 (d.J-8Bz.lB); 3.7-

4.3 (a.2B); and 2.3-3.0 (a).

Acetylation with pyridine-acetic anhydride and preparative

TLC (Si-gel. benzene-acetone. 4:1. v/v. Rf 0.36). gave an off-

white solid. lB-NMR in CDC13: ~ 6.9-7.25 (m); 6.59 (s.lB);

6.52 (s.lB); 6.20 (a.lB); 5.88 (s.lB); 5.85 (a.1B); 4.9-5.25

(m); 2.4-2.9 (a); and 1.25-2.2 (a).

2-Furvl-(6-catecbinyl)-8-catecbinyl) .tbane (B)

The isomeric 2-furyl-di-(catecbinyl) .tbane (B) was obtained

frC8 the same mixture by collection of the peak on HPLC eluted at

a retention volume of 28.6 mI. Two diaensional cellulo8e TLC

showed that the product obtained by preparative HPLC was

predominantly one compound at Rf (A) 0.60 and Rf (B) 0.75. Found:

C, 57.5; H, 5.1%; C35H300l3.4H20 require8 C, 57.5; H, 5.2%.

lH~ in acetone-d6: ~ 7.6-8.3 (br,OH); 7.20 (_,lH); 6.7-6.95

(m,6H); 6.45 (8,lnH); 6.40 (s,~H); 6.25 (8,lnH); 6.16 (_,lH); 6.14

(s,2H); 5.97 (m,lH); 5.76 (m,~H); 4.65 (d,J-8Bz,lH); 4.57

(d,J-8Rz,lH); 3.8-4.2 (m); and 2.3-3.0 (-).

151{;ONDENSED TANNINS

Acetylation wi~b pyridine-acetic anhydride and preparative

TLC on Si-ge1 as before gave the deca-acetate at If 0.40. 1B-NMR

in CDC13: ~ 6.9-7.3 (-.6B); 6.56 (s.lB); 6.53 (s.lB); 6.20

(m.1B); 5.90 (m.1B); 5.85 (s.lB); 4.90-5.3 <a.3B); 4.75

(d.J-8Hz.1B); 3.85 (8.2ft); 2.4-3.1 (m.4B); and 1..25-1.30 <a).

ACKN(MLEDGMERTS

We thank the O\enlistry Division, Department of Scientific

and Industrial Research and the Southern Forest Exper~ent Station

USDA-Forest Service, for the financial support of L. Y. Foo while

on study leave at the Southern Forest Experiment Station. We also

thank Dr. R. H. Newman, Chemistry Division, DSIR, for solid state

13c-NMR spectra; Dr. L. L. Ingram, Mississippi State University,and Dr. J. J. Karchesy, Oregon State University, for MS; and Mr.

Elmer Eskola for technical assistance in preparative HPLC.

REFERENCES

4.

s.6.

7.8.

9.

10.

u.

A. Pizzi. D. duT Ro88ouw l and G.M(E. Daling. Holzforschung

und Holzverwertung. 1!. 01 (1980J.

E. Pulkinnen. personal communication. 1980.

S.S. Kelly. R.A. Young. R.M. RammonL and R.H. Gillespie.J. Wood Chem. and Techn.. 1. 317 (1~82).

J.B. Barr and S.B. Wallon. J. Applied Polym. Sci.. 15. 1079(1971). -J. Milkovic, G.E.Meyers. and R.A. Young. Cell. Chem. andTechn..!. 051 (1979).

G.E~ Haciel and I.S. Chung. Macromolecules. 15. 1218(1902). .-

A. Gandini. Advances in Polym. Sci. &.49 (1977).

G.W. McGraw and R.W. He.in~ay. J. Cbea. Soc. PerkinTrans. I. 973 (1982).

L.Y. Foo and L.J. Porter. J. Chem. Soc. Perkin Trans. I. in

press.H.K.L. Hundt and D.G. Roux. J. Che.. Soc. Perkin Trans. I.1227 (1981).

T.J. Batterham and R.J. Highet. Aust. J. Chem.. 17. 428(1964). -R.W. Hemin~ay. J.J. Karchesy. G.W. McGraw, and R.A.Weilesek. Phytochem.. !!. 275 (1983).

u.

158 FOO AND HEMINGWAY

13.

14.

15.

16.

Use of t~ade names does not constitute endorsement byUSDA.

L.J. Porter, R.H. Newman, L.Y. Foo, H. Wongl and R.W.Hemingway, J. Chem. Soc. Perkin Trans. I, 1~17 (1982).

A.H. Fawcett and W. Dadamba, Kakromol. Chem., 183, 2799(1982). -R,W( Hemingsay ~d G.W. McGraw, J. Wood Chem. and Techn.31.4): 421 ~19~3}..

Editors

DONALD C. JOHNSONWeyerhaeuser Company

Tacoma, Washington 98477

LELAND R. SCHROEDERThe Institute of Paper ChemistryAppleton, Wiscon.rin 54912

Editorial Advisory Board

H. I. BOLKER, Pulp and Paper Research ImtitUte of Canada, Pointe ('laUe, QuebecD. L. BRINK, Unillenity of California, RichmondH. CHANG, North Carolina State Unillenity, RaleighJ. DEF AYE, Centre de Recherches .ruT Ie, Macromolecule, Vegerales, Francec. W. DENCE, Stilte University of New York, SyracuseG. GELLERSTEDT, Swedish Forest Productl Laboratory, StockholmJ. GIERER, SwediIh Forest Product, Laboratory, StockholmL S. GOLDSTEIN,North Carolina State Unillen#ty, RaleighD. A. I. GORING, Pulp and Paper Relearch InstitUte of Canada, Pointe aaiI'e, QuebecJ. S. GRATZL, North Carolina State Unillerlity, RaleilhW. M. HEARON,BoiIe Ca,cade Corporation, Portland, OregonR. W. HEMINGWAY, USDA Forest Serllice, Pinellille, LoldlianaT. HlGUCHI,Kyoto UniJIersity, JapanH. L. HINTZ, We'tllaco Corporation, North Charlaton, South CarolinaL. L. LANDUCCI, USDA Forest SerIIice, Madilon, WilconlinM. LEWIN, Iwael Fibel' InmtUte, Jeru.wlemJ. L. MINOR, USDA FOI'eIt Sel'l'ke, M.dilOn, WilconlinJ. NAKANO, Univerlity of Tokyo, JapanP. F. NELSON, Aust1'lJlian Pulp Manufacture,., Ltd., Melbourne, VictoriaH. H. NlMZ, Unil'erlity of Kal$I'Uhe, GeI'm4nyR. A. P ARHAM,/TT Rayonier, Inc.. Shelton, Walhin,ronA. PIZZI,National Timber Releal'ch InmtUte, Pretoria, South AfricaJ. POLCIN, CSR - Pulp and Paper Research InltitUte, CzecholioNk/aA. R. PROCTER, MacMillan Bloedel Ltd., VancoUller, B. C, CanadaO. SAMUELSON, Chalmerl Unillen#ty of Technology, GothenbUl'g, SwedenK. SARKANEN, Unillenity of Washington, SeattleJ. SCHURZ,Unillersity of Graz, AustriaN. SHIRAISHI, Kyoto Unillenity, JapanR. P. SING!!.. Scott Paper Company, Philadelphia, PennrylNniaE. SJ~STROM,Hel.rinki Unive1'lity of Technology, FinlandE. J. SOLTES, Texa, A 6. M Unillenity, CoUege StationN. S. THOMPSON, 11Ie InltitUte of Paper Chemistry, Appleton, WilconsinK. WARD, JR., Appleton, WilconsinE. ZA VARIN, Unillerlity of California, Richmond