DUNSTAN AND MUSSELL : APPLICATION OF VISCOMETRY, ETC. 565

LXV I I- The Application Measurement oj the

o f Viscornetry to Rate o f Reaction.

the

By ALBERT ERNEST DUNSTAN and ALBERT GEORGE MUSSELL.

SINCE the viscosity-coefficients of different substances vary between wide limits, it is possible to follow the course of a reaction, provided that there is sufficient variation in this property in the initial and final states. The application of physical methods t o this end is already well known, and it will be sufficient briefly to notice the work of Patterson and McMillan in this direction. These authors (Trans., 1907, 81,604; 1908, 93, 1041) took advantage of the fact that the rotation of ethyl tartrate is eminently sensitive to the presence of foreign substances. It varieo largely, for example, when ethyl tartrate is dissolved in different rolvents ; and, conversely,

Publ

ishe

d on

01

Janu

ary

1911

. Dow

nloa

ded

by U

nive

rsity

of

Mas

sach

uset

ts -

Am

hers

t on

27/1

0/20

14 0

6:28

:33.

View Article Online / Journal Homepage / Table of Contents for this issue

566 DUNSTAN AND MUSSELL : THE APPLLCATIOX OF VISCOMETRY

when an isodynamically changing compound is dissolved in this active liquid, the rotation changes in sympathy. In accordance with this, the above-mentioned authors measured the velocities of isodynamic change for benzsynaldoxime -+ benzan tialdoxime ; piperonalsynoxime --+ piperonalantioxime ; o-isonitrotoluene -+ w-nitrotoluene, and several similar cases. An important point brought out, which militates against the utility of this method for comparison purposes, is that the more highly purified ethyl tartrate afforded constants different from those given by the slightly less pure solvent, and, further, OF course, the changing substance must be soluble in the ethyl tartrate.

The change of viscosity during a reaction has been used to follow the effect of heat on gelatin solutions (von Schroeder, Zeitsch. physikal. Chem., 1903, 45, 75). This author found dy/dt= K((yl - yz), where q2 is the final value of the viscosity, so that if the total viscosity change be taken as a measure of the chemical change, it is obvious that a unimolecular reaction is here indicated. Beck, Trietsche, and Ebbinghaus (Zeitsch. physikal. Clhem., 1907, 58, 425) also pointed out that change in viscosity might be utilised for the measurement of the velocity of a reaction.

I n the present communication the authors have endeavoured to show that the viscomet.ric method is applicable to a variety of chemical reactions, and probably to all, could the conditions be suitably governed. The following changes were found to be capable of measurement:

Freshly distilled acetoacetic ester (enolic) --t equilibrium mixture ; aniline -+ phenylthiocarbamide ; ammonium thiocyanat e -+ thiocarbamide ; ammonium cyanate -+ carbsmide ; acetic anhydride -+ acetic acid ; bnzoyl chloride -+ benzoic acid ; hydro- lysis of benzspaldoxime.

(1) The Change of Viscosity of Freshly Distilled Ethyl Acetoacetate.

Schaum (Ber., 1898, 31, 1964) first showed that acetoacetic ester He made the following underwent a change of density on keeping.

determinations : Density, Density,

Fresh distilled. after 6 hours. after 24 hours. 1 -0278 1 '0282 1.0282 1.0278 1.0284 1'0284 1.0265 1.0269 1.0270

A more complete study of this change has been carried out for

The ester was purchased from Kahlbaum. It boiled at 137O/ us by Mr. Thole, with the following results.

240 mni. It was distilled at -6h. 25m. p.m.

Publ

ishe

d on

01

Janu

ary

1911

. Dow

nloa

ded

by U

nive

rsity

of

Mas

sach

uset

ts -

Am

hers

t on

27/1

0/20

14 0

6:28

:33.

View Article Online

TO THE MEASUREMENT OF THE RATE O F REACTION. 567

Ti me h. m. Deiisity 25/4. 6 36 1.02094 6 42 6 49 1.02119 7 6 1.02123 7 9 7 15 i 23 1.02125 7 35 7 42 1'02128 i 48 8 2 1 '021 28 8 50 1.02128

-

- -- -

-

Viscosity.

0'015330 0'015340

0.015367 0'015376

0.015385

0.015393

-

-

- -

a - x.

0 -000063 0.000053

0 *000026 0.000017

0 *000008

-

-

-

Average .....

- 1 . l o g - . t a-x

- 0'0246

0-0327 0,0395

0,0389

-

-

-

The densities required for this calculation of the viscosity- coefficients are interpolated from the curve drawn through the experimental points.

1 a Considering the very small differences, the values of - . loge--- t a-x

are surprisingly constant.

(2) Aniline Heated with Ammonium Thiocyanate t o Form Ph enyl t h.iocarbamide.

A hot saturated solution of ammonium thiocyanate was made in aniline. This was filtered into the viscometer heated to 130° in an oil-bath. Many experimental difficulties were met with, notably in the streams of bubbles evolved, which choked the capillary. The crude phenylthiocarbamide which separated on treating the rea&ion mixture with dilute hydrochloric acid melted a t 149O.

- 1 . 1 o g , a . Time (idns.). Time of flow. a - x. t a--2

0 177.2 - - 4 171.2 5.8 0.177 7 168.6 3'2 0-3 86 11 167 -0 1-6 0.161 15 165.6 0'2 0'211 19 165.4 - --

Average ...... 0'184 The probable cause of the reaction is the formation of thiocarb-

amide, which reacts with the large excess of aniline present to yield the phenyl derivative. In each case a unimolecular constant should be given.

(3) Rate of Change of Ammonium Thiocyanate t o Thiocarbamide.

Attempts were made at first to follow this reaction by allowing the melted thiocyanate to remain for several hours in the viscometer, immersed in an oil-bath, the temperature of which was kept constant at about 1 6 0 O . Insuperable difficulties were met with, however,

Publ

ishe

d on

01

Janu

ary

1911

. Dow

nloa

ded

by U

nive

rsity

of

Mas

sach

uset

ts -

Am

hers

t on

27/1

0/20

14 0

6:28

:33.

View Article Online

568 DUNSTAN AND MIJSSELL : 1 HE APPLICATION OF VISCOMETRY

in the streams of bubbles which passed up through the capillary. Better results were obtained when the ammonium thiocyanate was heated in an oil-bath in a corked flask at a constant temperature. Samples were withdrawn every stated interval, and as they solidified immediately, i t would he taken as certain that the reaction termin- ated at the time of removal of the sample.

One gram of the sample was dissolved in 12 C.C. of water, and the viscosity determined immediately after filtration into the visco- meter.

Temperature of oil-bath 1 6 0 O . One gram of product dissolved i n 12 C.C. of water.

T ime of withdrawal (in hours),

0 1 2 4 7 11.6

Time of flow ( in seconds).

230.0 231.5 233.0 235.0 236.0 236'1"

Pure thiocarbamide.. , . . . .. . , . . , , . . . . , , 248 *O Thiocarbamide heated 1 hour ...... 240.0

7 9 ,, 39 hours ... 236'0 * Part of product was insoluble and odour of hydrogen sulphido was observed.

When these results are plotted, it is found that they lie on two curves which approach each other. The viscosity at equilibrium is 236, and this corresponds with an equilibrium mixture of 33 per cent. of thiocarbamide.

Polarimetrically, Patterson and McMillan (Zoc. c i t . ) obtain 45 per cent., whilst Werner and Reynolds (Trans., 1903, 83, 1) found 24-72 per cent. (at temperatures between 170° and 180O).

(4) Rate of Change of Ammonium Cyanate into Carbamide.

Very many experiments have been made on the measurement of this reaction. It has been found best tomix two cold equivalent saturated solutions of ammonium sulphate and potassium cyanate, filter off the precipitated potassium sulphate, and, on cooling, further to filter the solution of ammonium cyanate into the visco- meter. A t the ordinary temperature (25O) the reaction proceeds slowly, yet measurably. A typical series is given below

Publ

ishe

d on

01

Janu

ary

1911

. Dow

nloa

ded

by U

nive

rsity

of

Mas

sach

uset

ts -

Am

hers

t on

27/1

0/20

14 0

6:28

:33.

View Article Online

TO THE MEASUREMENT OF THE RATE OF RDACTION. 569

Solution made at 9.40 a.m. Time

(mins.). Time of observation. 0 Wednesday 10.10 a.m.

50 2 , 11.0 9 ,

120 ,, 12.10 p.m. 238 > 9 2.8 $ 9

247 9 , 2.17 ,, 290 9 , 3.0 9 ,

350 Y , 4.0 1 ,

560 ¶, 7.30 ,, Following Saturday.., 12.30 ,,

Time of Cow. 4/29’’ 4’30” 4‘32” 4 ’3 4 ‘6” 4’35 -0” 4’36.0“ 4’38 ’0” 4’4 5 *Of’ 5’5 -0”

1 a - z* t Iogloa+z- 36.0 L

35.0 0*00024 33.0 0.00031 30 *4 0.00031 30.0 0 *00032 29’0 0-00032 26‘7 0.00037 20.0 0-00045 - -

These values for R sufficiently confirm the experimental work of Patterson (Zoc. c i t . ) , Walker, Hambly, Kay, and Wood (Trans., 1895, 67, 746; 1897, 71, 489; 1898, 73, 21) that this reaction is not of the first order.

( 5 ) Effect of Alkali on p-Nitrophenylacetonitrile.

We are indebted to Mr. F. G. Pope, of East London College, for a supply of the above compound. On being dissolved in absolute alcohol, it gives a, colourless solution, which, with a little alcoholic potassium hydroxide, turns to red, After several hours it darkens considerably, and on pouring into water, becomes emerald-green. It is possible that hydrolysis of the nitrile group goes on, followed by intramolecular change to a substance of the formula:

O : N : / T : C H * C O .

I 1 \-/ 0

A saturated solution was made in ethyl alcohol, to which wa added a few drops of alcoholic sodium hydroxide. The times of flow were plotted against times of observation, and a regular curve drawn through. The following results were obtained from inter- polated values :

Time (mins.). a - z (in & seconds). 0 63 5 41 10 32 15 25 20 18 25 16 30 11 35 9 40 6

‘t . log,,“. a-2

- 0.0373 0.0294 0.0267 0 *027 2 0.0249 0.0252 0.0241 0.0255

Average.. . . . . . . . 0.0288

The reaction apparently tends to the first order after the first ten minutes.

Publ

ishe

d on

01

Janu

ary

1911

. Dow

nloa

ded

by U

nive

rsity

of

Mas

sach

uset

ts -

Am

hers

t on

27/1

0/20

14 0

6:28

:33.

View Article Online

570 DUNSTAN AND MUSSELL : APPLICATION OF VISCOXETRY, ETC.

( 6 ) The Hydration. of Acetic Anhydride in Acetic Acid Solution.

Many preliminary experiments have been carried out with the intention of studying the rate of hydration of acetic anhydride with the equivalent weight of water, both dissolved in pure acetic acid. As we are still working on this reaction, one set only will be here quoted.

5 C.C. acetic acid (frozen out repeatedly). 4-72 C.C. acetic anhydride (b. p. 135"/739 mm.). 0.90 C.C. of water.

Time (niins. ).

0 15 22 37 45 52 65

115

Time of flow (secs. ). 158.0 159.0 159'6 160'4 161-2 161.4 161.0 164.6

a - x. 6.6 5 *6 5.0 4'2 3 '4 3'2 2 '6 -

Average ...

1 t C c - - 2

0.0048 0.0054 0.0053 09064 0.0060 0.0062

... ... ... ... 0.00568

- . lO,a,,_n- *

-

- --

Our experiments indicate that the abme reaction is by no means so simple as might be supposed, for at some concentrations the velocities of efflux become less as time goes on, whilst the absolute viscosities may rise to a maximum, and then steadily fall. This is shown in the accompanying table.

5 C.C. of acetic asid. 4-72 C.C. of acetic anhydride.

Time, Viscosity. 13.22 p.m. 0.01370 12.31 ,, 0'01374 12.44 ,, 0.01377 12.57 ,, 0 -01383 3.12 ,, 0.01395 4.14 ,, 0-01396

0.45 C.C. of water.

Time. Vis osity. 4.32 p.m. 0.01 379 6.26 ,, 0-01368 7-8 $ 3 0,01365 7.54 *, 0'01362 9.5 9 , 0.01353 9.35 ,, 0.01352

( 7 ) The Hydrolysis of Benzoyl Chloride in Aqueous Acetone. Benzoyl chloride being not sufficiently soluble in water, a solution

in aqueous acetone was made up of t.he following molecular concen- trations : acetone, 100 ; water, 203.4 ; benzoyl chloride, 5.2.

Time ( mins. ). 11.5 14-5 22'5 44'5 63 *o 80-0 140.0

I - . l o g - Time of flow. 1 a - X'

406.2 - 412'2 0-00952 425 '4 0.01025 441 '0 0.00954 444.2 0-00956 448 '0 0.01030 449'0

0 *00983 --

Average.. . . , , . . .

Publ

ishe

d on

01

Janu

ary

1911

. Dow

nloa

ded

by U

nive

rsity

of

Mas

sach

uset

ts -

Am

hers

t on

27/1

0/20

14 0

6:28

:33.

View Article Online

SYNTIIESIS OF DIPEPTIDES OF a-AMINOLAURIC ACID 571

Interpolated from curue :

19.3 34.0 64 0

0'00954 0'00954 0-00956

The benzoyl chloride was recovered in the form of benzoic acid at the end of the experiment.

We have also made a number of experiments with the syn-oximes. We hoped to follow the transformation of these substances into their anti-isomerides, but up to the present have found no means of inducing the change. Benzsynaldoxime, for example, is a very stable compound. It can be crystallised unchanged from hot alcohol, benzene, or amyl acetate, or even from hot water, so that our expectation that it would be converted into the anti-aldoxime in solution was not realised.

I n conclusion, we wish to thank hlr. A. S. Wood and Mr. A. Perry for their assistance with the experiments on the oximes and benzoyl chloride respectively.

PHYSICAL CHEMICAL LABORATORY, EAST HAN TECHNICAL COLLEQE.

Publ

ishe

d on

01

Janu

ary

1911

. Dow

nloa

ded

by U

nive

rsity

of

Mas

sach

uset

ts -

Am

hers

t on

27/1

0/20

14 0

6:28

:33.

View Article Online