Survey of Industrial Chemestry - Chapter 10

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Chapter 10

Chemicals from Propylene and Butylene

As we learned in Chapter 8, the official production of propylene isusually abo ut half that o f ethylene, only because a large part o f the propyleneis used by petroleum refineries internally to alkylate gasolines. This captive

use is not repo rted. Of the propylene used for chemical manufacture, nearly40% is po lymerized to po lypropylene, to be discussed in a later chapter. Othe remaining amount of propylene, seven chemicals from the top 50 aremanufactured. These are listed in Table 10.1. Their industrialmanufacturing methods are summarized in Fig. 10.1. Note that four of thesechemicals, cumene, pheno l, acetone, and bisphenol A, are also derived froma second basic o rganic chemical, benzene.

1. ACRYLONITRILE 2-PROPENONITRILE)

CH 2 =CH-C=N

Table 10.1 Propy lene Derivatives in the Top 50

AcrylonitrilePropylene OxideCumenePhenolAcetone

Bisphenol Aft-Butyraldehyde



propylene acrylonitrile

propylene oxidestyrene

cumene phenol acetone

bisphenol A

fl-butyraldehyde isobutyraldehyde

Figure 10.1 Synthesis o f propylene derivatives in the top 50 chemicals.

Acrylonitrile and other three-carbon analogs containing a double bondhave a common name derived from the word acrid meaning strong anddisagreeable, in regard to the odor of most of these chemicals. Co mpoundsin this family are given here with their common names.

acrylonitrile

acrylic acid



acrolein

acrylamide

Acrylonitrile was made completely from acetylene in 1960 by reactionwith hydrogen cyanide. For some years ethylene oxide was the raw materialfor addition of HCN and elim ination o f H 2O.

Neither of these methods is used today. A round 1970 the industryswitched from C2 raw materials and classical organic chemical additionreactions to the ammoxidation of propylene. Now all acrylonitrile is madeby this procedure, which involves reaction of propylene, ammonia, anoxygen at 400-45O0C and 0.5-2 atm in a fluidized bed Bi2O3^nMoO3

catalyst. The yield is approximately 70%.

2CH 2=CH-CH 3 + 2NH3 + 3O2 2CH 2 =CH-C=N + 6H2O

The mechanism is undoubtedly a free radical reaction that occurs veryeasily at the allyl site in propylene, forming the resonance-stabilized allylradical.

CH 2=CH-(̂ H 2 ^H 2 -CH=CH 2

By-products of this reaction are acetonitrile, CH 3 -C=N, and hydrogencyanide. This is now a major so urce of these two m aterials. Interestingly,th e C2 by-product acetonitrile has a bp o f 81.6 0C, whereas acrylo nitrile w iththree carbons has a lower bp of 77.3 0 C, quite an unusual reversal of thisphysical property's dependence on molecular weight. The TWA ofacrylonitrile is 2 ppm and it is on the list of Reasonably Anticipated to BeHuman Carcinogens.

Table 10.2 ou tlines the uses of ac rylon itrile. One impo rtant use oacrylonitrile is in the po lymerization to polyacrylonitrile. This substance andits copolymers m ake good synthetic fibers for the textile industry. Acrylic isthe fourth largest produced synthetic fiber behind polyester, nylon, an



Table 10.2 Uses of A crylonitrile

Adiponitrile 33%

Ac rylic fibers 25ABS/SA resins 23Acrylamide 9

Nitrile elastom ers 3Miscellaneous 7

Source: Chemical Profiles

polyolefm. It is known primarily for its warmth, similar to the natural andmore expensive fiber w oo l. Approximately 23% o f the acrylonitrile is madeinto plastics, including the copolymer of styrene-acrylonitrile (SA) and theterpolymer of acrylonitrile, butadiene, and styrene (ABS). A crylamide has afast-growing use as a flocculent for water treatment units. Exports ofacrylonitrile are over 1 billion Ib/yr.

The largest use of acrylonitrile is the manufacture of adiponitrile, madeby two different methods. One method is by the electrohydrodimerization oacrylonitrile. It is converted into hexam ethylenediam ine (HM DA ), w hich used to m ake nylon. The other adiponitrile synthesis is C4 chemistry, w hichwill be discussed later in this chapter, Section 8.

2CH 2 =CH-C=N -^- N=C-(CH2)

4-C=N — H 2 N-(CH 2 ) 6 -NH 2

2e'

acrylonitrile adiponitrile HMDA

About one third of all adiponitrile is made from acrylonitrile. In theelectrodimerization o f acrylonitrile a two-phase system is used containing aphase transfer catalyst tetrabutylammonium tosylate [(W-Bu)4N

+OTs"]. Thehead-to-head dimerization may be visualized to occur in the followingmanner.



The by-product of acrylonitrile manufacture, HCN, has its primary use inthe manufacture o f methyl methacrylate by reaction with acetone. This iscovered later in this chapter, Section 4.

2. PROPYLENE OXIDE 1,2-EPOXYPROPANE)

There are two important methods for the manufacture of propylene oxide,each accounting for one half the total amount produced. The older methodinvolves chlorohydrin formation from the reaction o f propylene withchlorine water. Before 1969 this was the exclusive method. Unlike theanalogous procedure fo r making ethylene oxide from ethylene, which now isobsolete, this method fo r propylene oxide is still economically competitive.Many old ethylene oxide plants have been converted to propylene oxidesynthesis.

The mechanism in the first step involves an attack of the electrophilicchlorine o n the double bond o f propylene to form a chloronium ion, which isattacked by a hydroxide ion to complete the first reaction. The dilute



chlorohydrin solution is mixed with a 10% slurry of lime to form the oxide,which is purified by distillation, bp 340C . The yield is 90%. Propyleneoxide has a TWA of 20 ppm and is on the list of "Reasonably Anticipated toBe Hum an Carcinogens."

A new variation of the chlorohydrin process uses /-butyl hypochlorite aschlorinating agent. The waste brine solution can be converted back tochlorine and caustic by a special electrolytic cell to avoid the waste ofchlorine.

The second manufacturing method for propylene oxide is viaperoxidation of propylene, called the Halcon process after the company thatinvented it. Oxygen is first used to ox idize isobutane to /-butyl

hydroperoxide (BHP) over a m o lybdenum naphthenate catalyst at 9O0C and

450 psi. This oxidation occurs at the preferred tertiary carbon because atertiary alkyl radical intermediate can be fo rmed easily.

Reaction

BHP

Mechanism

(1)

(2)

(3)

The BHP is then used to oxidize propylene to the oxide. This reaction ionic and its mechanism follows. The yield of propylene oxide frompropylene is 90%.

Reaction



The /-butyl alcohol can be used to increase the octane of unleaded

gasoline or it can be made into methyl /-butyl ether (MTBE) for the sameapplication. The alcohol can also be dehydrated to isobutylene, which inturn is used in alkylation to give highly branched dimers for addition tostraight-run gasoline.

Since approximately 2.2 Ib of/-butyl alcohol would be produced per 1 Ibof propylene oxide, an alternative reactant in this method is ethylbenzenehydroperoxide. This eventually forms phenylmethylcarbinol along with the

propylene oxide. The alcohol is dehydrated to styrene. This chem istry wascovered in Chapter 9, Section 6 as one of the syntheses o f styrene. Thus tside product can be varied depending on the demand for substances such as/-butyl alcohol o r styrene. Research is being done on a direct oxidation propylene with oxygen, analogous to that used in the manufacture ofethylene oxide from ethylene and oxygen (Chapter 9, Section 7). But theproper catalyst and co nditions have no t yet been found. The methyl group isvery sensitive to oxidation conditions.

As an aside to the manufacture of propylene oxide via the chlorohydrprocess let us mention use o f this type o f chemistry to make epichlo rohydr

Mechanism

allyl chloride

epichlorohydrin



Table 10.3 Uses of Propylene Oxide

Polypropylene glycol 60%

Propylene glycol 25

Glycol ethers 4Miscellaneous 11


Although not in the top 50, it is an important monomer for making epoxyadhesives as well as glycerine (HO-CH 2-CHOH-CH 2-OH). Propylene isfirst chlorinated free radically at the allyl position at 50O0C to give ally 1chloride, which undergoes chlorohydrin chemistry as discussed previously togive epichlorohydrin. The student should review the m echanism of allyl freeradical substitution from a basic organic chemistry course and also work outthe mechanism for this exam ple of a chlo rohydrin reaction.

Table 10.3 summarizes the uses of propylene oxide. Propylene glycol ismade by hydrolysis of propylene oxide. The student should develop themechanism for this reaction, which is similar to the ethylene oxide to

ethylene glycol conversion (Chapter 9, Section 8). Propylene glycol is amonomer in the manufacture of unsaturated polyester resins, which are usedfor boat and automo bile bodies, bow ling balls, and playgroun d equipm ent.

But an even larger use of the oxide is its polymerization topoly(propylene glycol), which is actually a polyether, although it has

propylene glycol propy lene oxiden = 7-35

poly (propylene glyco l)

a po lyurethane



hydroxy end groups. These hydroxy groups are reacted with an isocyanatesuch as toluene diisocyanate (TDI) to form the urethane linkages in the highmolecular weight polyurethanes, useful especially as foams fo r automobileseats, furniture, bedding, and carpets. Po ly(propylene glyco l) is used tomake both flexible and rigid polyurethane in a 90:10 market ratio.

3. CUMENE ISOPROPYLBENZENE)

Cumene is an important intermediate in the manufacture o f phenol andacetone. The feed m aterials are benzen e and pro pylen e. This is a Friedel-Crafts alkylation reaction catalyzed by solid phosphoric acid at 175-2250Cand 400-600 psi. The yield is 97% based on benzene and 92% o n pro pylene.Excess benzene stops the reaction at the monoalkylated stage and preventsthe polymerization o f propylene. The benzene:propylene ratio is 8-10:1.

(excess)

Interestingly, if benzene is left out similar conditions are used tomanufacture the trimer and tetramer of propylene. The cumene is separatedby distillation, bp 153 0 C.

The mechanism of the reaction involves electrophilic attack of thcatalyst on the double bond of propylene to form the more stable secondarycation, which reacts with the T cloud o f benzene to give a delocalized ion.

Deprotonation rearomatizes the ring.



A major industry shift to zeolite-based catalyst systems is expected tolower production costs and improve produc t yield.

Approximately 95% of the cumene is used to make phenol and acetone.A small amount is used to make a-m ethylstyrene by dehydrogenation. Thismaterial is used in small amounts during the polymerization of styrene tovary the properties of the resulting copolymer.

catalyst

4. ACETONE 2-PROPANONE)

Presently there are two processes that make acetone in large quantities.The feedstock for these is either isopropyl alcohol or cum ene. In the last fewyears there has been a steady trend away from isopropyl alcohol and towardcumene, but isopropyl alcohol should continue as a precursor sincemanufacture o f acetone from only cumene would require a balancing of themarket w ith the co -product pheno l from this process.

This is not always easy to do, so an alternate acetone source is require

In fact, isopropyl alcohol may become attractive again since cumene can bused to increase octane ratings in unleaded gasoline, and phenol, as aplywood adhesive, has its ups and downs with the housing industry. Thepercentage distribution o f the two methods is given in Table 10.4.

In the minor route isopropyl alcohol, obtained from the hydrolysis ofpropylene, is co nverted into acetone by either dehydrogenation (preferred) orair oxidation. These are catalytic processes at 50O0C and 40-50 psi. Theacetone is purified by distillation, bp 560C . The conversion per pass is 70-85% and the yield is over 90%.

Table 10.4 Manufacture of A cetone

Year From Isopropyl Alcohol From Cumene

1959 80% 20%

1975 46 541985 15 851999 6 94



dehydrogenation

air oxidation

The main route, the formation of phenol and acetone from cumenhydroperoxide, involves a fascinating rearrangement o f cumenehydroperoxide where a phenyl group migrates from carbon to an electron-deficient oxygen atom . This was discovered by German chem ists Hock anLang in 1944 and commercialized in 1953 in the U.S. and U.K. Thehydroperoxide is made by reaction of cumene with oxygen at 110-1150Cuntil 20-25% of the hydroperoxide is fo rm ed. The oxidation step is similto that o f cyclohexane to cyclohexane hydroperoxide and will be treated inChapter 11, Section 4. Students should be able to work out this mechanismon their ow n with this help Co ncentration o f the hydroperoxide to 80% followed by the acid-catalyzed rearrangement at 70-8O0C. The overall yie ld

is 90-92%.

cumene cum ene hydroperoxidephenol

acetone

Side products are acetophenone, 2-phenylpropan-2-ol, and a-methylstyrene. Acetone is distilled first at bp 560C . Vac uum distillation

acetophenone 2-phenylpropan-2-ol oc-methylstyrene

recovers the unreacted cumene and yields a-methylstyrene, which can behydrogenated back to cum ene and recyc led. Further distillation separat



phenol, bp 1810C, and acetophenone, bp 2020C. The weight ratio ofacetone:phenol is 0 .6:1.0.

The mechanism of the rearrangement is an excellent practical industrialexample of a broad type of rearrangement, one occurring with an electron-deficient oxygen. The mechanism is given in Fig. 10.2.

cumene hydroperoxide a protonated hydro perox ide

s

m

no

resonance stabilized

a hem iketal

phenolresonance stabilized

acetone

Figure 10.2 Mechanism of the cum ene hydroperox ide rearrangement.



Table 10.5 Uses of Acetone

Acetone cyanohydrin 45%

Bisphenol A 20Solvent 17Aldo l chemicals 8

Miscellaneous 10


Table 10.5 gives the uses of acetone. A very important organic chemicalthat jus t missed the top 50 list, methyl methacrylate, is made from acetone,methanol, and hydrogen cyanide. Approximately 1.2 billion Ib of thiscompound is manufactured and then polymerized to poly(methylmethacrylate), an important plastic known for its clarity and used as a glasssubstitute. The synthesis is ou tlined as follow s.

methyl methacrylate

The first reaction is a nucleophilic addition of HCN to a ketone, thesecond is a dehydration of an alcohol and hydrolysis of a nitrile, and the

third is esterification by methanol.Aldol chemicals refer to a variety of substances desired from acetoneinvolving an aldol condensation in a po rtion of their synthesis. The mosimportant of these chemicals is methyl isobutyl ketone (MIBK), a commonsolvent for many coatings, pesticides, adhesives, and pharmaceuticals.Approximately 0.17 billion Ib o f MIBK were made in recent years. Thesynthesis is o utlined on the next page.



diacetone alcohol mesityl oxide

MIBK

Diacetone alcohol is a solvent used in hydraulic fluids and printing inkRecall that the aldol condensation is an example of a variety of carbanionreactions used to make large molecules from smaller ones. An aldehyde or aketone with at least one hydrogen on the carbon next to the carbonyl willreact to give the aldol condensation. The mechanism is given as fo llow s.

5. BISPHENOL A BPA)

Bisphenol A is manufactured by a reaction between phenol and acetone,the two products from the cum ene hydroperox ide rearrangement. Thetemperature of the reaction is maintained at 5O0C for about 8-12 hr. A slurry



of BPA is formed, which is neutralized and distilled to remove excessphenol. Some o p isomer is formed along with the predominance of p pisomer.

bisphenol A

The student should develop the mechanism of this reaction using thfollowing stepwise info rmation : (1) protonation of the carbonyl; (2electrophilic attack on the aromatic ring; (3) rearomatization by proton lo(4) another protonation, but then loss of a water molecule; and (5)electrophilic attack and rearom atization .

The major uses of BPA are in the production of polycarbonate resin(63%) and epoxy resins (27%). Po lycarbonates have major outlets inautomotive parts, compact discs, eyeglasses, and sheet and glazingapplications, and have caused bisphenol A co nsumption to m ore than do ubduring the past decade. Epoxy resins are two -component adhesives for verstrong bonding. M iscellaneous uses include flame retardants (mostlytetrabromobisphenol A) and other po lymer m anufacture. Polycarbonagrade bisphenol A is >99% p p isomer. The epoxy grade is 95% p p. Thep p and o p isomers can be separated by a combination of distillation andcrystallization.

6. H-BUTYRALDEH YDE BUTANAL)

Butyraldehyde is made from propylene by the oxo process, also know n ashydroformylation. Synthesis gas (CO + H2) is catalytically reacted withpropylene to the butyraldehydes. The approximate yields are 67% n-butyraldehyde and 15% isobutyraldehyde.

H-butyraldehyde isobutyraldehyde



The classic oxo catalyst is octacarbonyldicobalt at 130-1750C and 250atm. This reacts with hydrogen to give hydridotetracarbonyl cobalt, theactive catalyst in the oxo process.

The mechanism of carbonylation/hydrogenation involves addition of thealkene to form a T complex, followed by alternating additions of H, CO, and

H.

Newer catalysts are being studied to increase the ratio of w-butyraldehydeto isobutyraldehyde.

The main use of w-butyraldehyde is the production of n-butyl alcohol byhydrogenation. w-Butyl alcohol is used for ester synthesis, especially butylacetate, aery late, and methacrylate, com mo n solvents for coatings.

butyl acetate butyl acrylate butyl m ethacrylate



7. CHEMICALS FROM THE C 4 FRACTION

Chemicals obtained from petroleum having four carbons aremanufactured at a considerably lower scale than ethylene o r propylenederivatives. Only five C4 co mpounds— butadiene, acetic acid, vinyl acetate,isobutylene, and methyl /-butyl ether (MTBE)—appear in the top 50. Themanufacture of butadiene and isobutylene, as well as the separation of otherC4 compounds from petroleum, is described in Chapter 8, Sections 3-5.Acetic acid was discussed as a derivative of ethylene in Chapter 9, Sectionand is discussed as a derivative o f methane in Chapter 12, Section 3. Vinyacetate was discussed in Chapter 9, Section 4. A few impo rtant derivative

o f C4 chemistry will be briefly mentioned here as well as M TBE.

8. BUTADIENE DERIVATIVES

Besides butadiene, another important monomer for the syntheticelastomer industry is chloroprene, which is polymerized to the chemicall

resistant poly chloroprene. It is made by chlorination of butadiene follow bydehydrochlorination. As with most co njugated dienes, addition occurs either1,2 or 1,4 because the intermediate allyl carbocation is delocalized. The 1,4-isomer can be isom erized to the 1,2-isomer by heating with cuprous chloride.

Reaction

15%NaOH-HCl10O0C

chloroprene

ntermediate

Another derivative of butadiene, hexamethylenediamine (HMDA), isused in the synthesis of nylon. We have already met this compound earlierin this chapter since it is made from acrylonitrile through adiponitrile.



Approximately tw o thirds of all adipo nitr ile is made from 1,3-butadiene and2 m oles of hydrogen cyanide. This is an involved process chem ically and itis summarized in Fig. 10.3. Bu tadiene first adds one mo le of HCN at 6O0Cwith a nickel catalyst via both 1,2- and 1,4-addition to give respectively 2-

methyl-3-butenonitrile (2M3BN) and 3-pentenonitrile (3PN) in a 1:2 ratio.The 1,2-addition is the usual Markovnikov addit ion with a secondarycarboc ation interm ediate being preferred . Fig. 10.4 show s an ADN reactoNext isomerization of the 2M3BN to 3PN takes place at 15O0C. Then moreHCN, more catalyst, and a triphenylboron promoter react with 3PN to form5% methylglutaro nitrile (M GN ) and m ostly a dipo nitrile (AD N). The A DN formed from 3PN prob ably through isom erization of 3PN to 4 -pentenonitril

and then anti-Markovnikov addition of HCN to it. The nickel catalyst mustplay a role in this last unusual mode of addition, and a steric effect may alsobe operating to make CN attack at the primary carbon rather than acationically preferred secondary carbon. A complicated set of extractionsand distillations is necessary to obtain pure ADN . Even then thehexamethylenediamine (HMDA) made by hydrogenation of A DN m ust alsobe distilled through seven columns to purify it before polymerization to

nylon. Fig. 10.5 pictures some HMDA distillation units.

Figure 10.3 Manufacture of adiponitrile and hexamethylenediamine from 1,3-butadiene.

ADN HMDA



Figure 10.4 Reactors used in the conversion of 1,3-butadiene and HCN to adiponitrile.(Courtesy of Du Pont)

Figure 10.5 Distillation co lumns associated w ith the purif icatio n of hexamethyl-enediamine. (Courtesy of Du Pont)



9. METHYL /-BUTYL ETHER MTBE)

In 1984 methyl /-butyl ether (MTBE) broke into the top 50 for the firsttime with a meteoric rise in production from 0.8 billion Ib in 1983 to 1.47billion Ib in 1984 to be ranked 47th. In 1990 it was 24th w ith production over6 billion Ib, and in 1995 it was 12th at 18 billion Ib. A full discussion of thecurrent economic status of MTBE is given in Chapter 7, Section 4 as theimportant gasoline oc tane enhancer. That is its only major use. MTBE ismanufactured by the acid catalyzed electrophilic addition of methanol toisobutylene.

or ionexchangecatalyst

MTBE

10. OTHER C 4 DERIVATIVES

An important antioxidant for many products is butylated hydroxytoluene(BHT), mo re properly named 4-methyl-2,6-di-/-butylphenol. Acid-catalyzedelectrophilic aromatic substitution of a /-butyl cation at the activatedpositions ortho to the hydroxy group of/?-cresol yields this product, p-Cresol is obtained from coal tar or petroleum.

BHT

For many years maleic anhydride (MA) was made from benzene byoxidation and loss o f two moles of CO2. Even as late as 1978 83% of maleic



anhydride was made from benzene. However, the new Occupational Safetyand Health Administration OSHA) standards for benzene plants requiredmodifications in this process, and butane is also cheaper than benzene. As aresult since 1989 all maleic anhydride is now made from butane. This hasbeen a very rapid and complete switch in manufacturing method.

The mechanism is not well understood, but the intermediates in theprocess are butadiene and furan. The uses of maleic anhydride are

furan

summarized in Table 10.6. Unsaturated polyester resins are its prime usearea. Food acidulants include fum aric and malic acids. Malic acid competeswith citric acid as an acidulant fo r soft drinks, and it is added to products thatcontain aspartame, the artificial sweetener, because it makes aspartame taste

more like sugar. Agricultural chemicals made from M A include daminozide(Alar®), a growth regulator fo r apples which in 1989 was found to becarcinogenic because of a breakdown product, unsymmetricaldimethylhydrazine UMDH). Alar® is needed to keep the apple on the tree,to make a more perfectly shaped, redder, f irmer apple, and to maintainfirmness in stored apples by reducing ethylene production.

Table 10 6 Uses of Maleic Anhydride

Unsaturated polyester resins 62%Lube o il additive 11

Copolymers 7Agricultural chemicals 4Fumaric acid 3Malic acid 3Miscellaneous 10




fumaric acid malic acid

daminoazide (Alar*) UDMH

The oxo process is used to convert the €4 fraction to C 5 derivatives.Synthesis gas is catalytically reacted with 1-butene to give pentanal whichcan be hydrogenated to 1-pentanol (w-amyl alcohol), giving a route to C 5

compounds in larger amounts than what would be available from C 5 alkanesin petroleum.

Suggested Readings

Chemical Profiles in Chemical Marketing Reporter, 7-29-96, 12-2-96, 3-20-98, 7-13-98, 1-4-99, 3-22-99, 4-5-99, 12-27-99, and 5-8-00.

Kent, Riegel s Handbook of Industrial Chemistry, pp. 830-846.Szmant, Organic Building Blocks of the Chemical Industry, pp. 265-378.Wiseman, Petrochemicals, pp. 65-88.Writeoff and Reuben, Industrial Organic Chemicals, pp. 149-224.

catalyst

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