485

QUANTITATIVE ESTIMATION AS ACETIC ACID OF ACETYL,ETHYLIDENE, ETHOXY, AND A-HYDROXYETHYL GROUPSI

Bv R. U. LBltrrux2 eNo C. B. PunvBs3

AbstractKuhn and L'Orsa's method for estimating terminal methyl and similar groups

was based on the recovery of the acetic acid formed lvhen such units wereoxidized with hot concentiated chromic acid solution. The method has nowbeen reduced to the sernimicro scale and refined to the point where good analysesfor acetl'I, ethylidene, ethoxy, and a-hydroxyethyl groups in a variety-o{ -sub-stances'are obtained. Acetylated triphenylmethl'l cellulose ethers, which donot seem amenable to customar]' acetyl analyses, give good results by thepresent procedure.

Introduction

During an extension of published $rork on the acctylation of cellulose trityl(triphenylmethyl) ether (5, 11, 12), standard methods of acetyl analysisproved to yield lorv results. Those tried q'ere the sodium methylate saponi-fication - p-toluenesulphonic acid - methanol distillation method of Cramer,Gardner, and Purves (1), the modification of the Ost distillation technique by'Genung and Mallatt (2), and saponification in a homogeneous medium as

described b1' Malm, Genung, Williams, and I'iie (9). Although all threemethods gave concordant and correct results in the absence of the trityl etherunit, in its presence each, although oftel fairiy reproducible in duplicate.estimations, lvas low by a variablc amottnt. Attempts made on samples

containing added triphenylmethl'l carbinol to determine the cause of these

aberrations led to no definite conclusion. In these circumstances attentionwas given to the oridations of organic substances by Kuhn ancl L'Orsa (7),

who employed a hot concentrated aqueogs solution of chromium trioxide.These authors found that in many cases a steam distillation of the oxidizingmixture recovered acetyl, cthoxy, and terminal mcthyl groups as acetic acid,the yield of acetic acid oftcn being more than 85/6 of theory. Their resultsrvere confirmed, for terminal methyl grottps in the lignin series, b-v ['{acGregor,Evans, and Hibbert (8). Ti-re present article describes a semimicro adaptationof the estimation, r,vhich gave practicaliy quantitative results. Although inblank runs the acidity of the distillate varied from 0.5 to 1.3 ml. of 0.02 i/alkali with slight variations in operating conditions, for a given apparatusand given reagents tiris blank was in a lixed ratio to the oxidizing equivalentof the distillate in terms of 0.02 I/ sodium thiosulphate solution. Ratios of1 . 33 to 1, and 0. 91 to 1, for example,.were observed rvitl-r two sets of equipmentused at different timcs. This blank acidit-v u/as presumably caused by

1 Monuscript receiaeil December 7, 1946.

Contri,bution Jrom the Dittision oJ Industr,iol and, Cellulose Chemistry, McG'i-ll _Un'iaersity,.Montreal, Que. From a th.esis presenied to the Faculty of Grailuate Studies-ond' Research byR. LI. Lemi.iur i,n September 19'ti in partiat futf,lmenl of the requirements Jor the degree of Doctor'oJ Phi.losophy.

2 Hold.er of Studentsh'ips under the National Research Council of Cary'dq, 1914-45, 1945-46.Present arl.dressi Departmeit of chenr.istry, Llni.versity oJ saskatchewan, saskotroon, sash.

3 E. B. Ettd.y Professor of Industrial ond Cellulose Chemistry, McGiIl' Uniuersily.

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486 :ANADIAN J}LiRNAL oF RESEARCH. voL. zs, sEC. B.

volatile impurities in the reagents and by the entrapment of traces of chromicacid in the distillate. Knor'ledge of the factor relating number of cubiccentimetres of alkali to number of cubic centimctres of thiosulphate in theblanks made it possible to dispense .with separatc blank determinations inroutine cstimations rvith the same equipment and reagents.

ReagentsDescription of the Method

1. Aqueous 30/6 chromium trioxidc,2. Carbon dioxide-free 0.020 -^/ sodium h)'droxide,3. Stanclard 0.020 ,V sodium thiosulphatc,4. Iodate-free potassium iodiclc,

5. Aqueous 10la sulphuric acid,6. Sodium bicarbonate,7. Indicator solutions: phenolphthalein, 7/6 am-vlose.

Procetl u re

A 15 tc 50 nrgm. san'rple (dcpenrling on tlre alnount of acetic acicl produced)rlas n'eighccl into a 100 ml. rouncl-bottonred flasl< equippecl t'ith a groundgiass joint (F'ig. 1). The sampic r",'a.s coverccl n'ith 10 ml. cf thc.30/6 chrornic

Frc. 1.

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LEM I E(J X AN D pU RV ES : QU AN T I T AT M EST I M AT ION OF ACET V L AN D OT E ER GROUPS 487

acid solution, the flask was two-thirds immersed in an oil-bath, the apparatus

(Fig. 1) was assembled, and nitrogen gas was passed through it at a rate of

on" to two bubbles per second. The temperature of the bath was then raised

to 155o C. within one-half hour by means of a hot-plate and was maintained

,at this figure until the end of the dctermination. 'loo rapid an initial rise in

temperature resulted in high bla.nks. Distillation began at 135o to 140'C'and, as successive 5 ml. volumes of distillate collected in the 50 ml' graduate,

5 ml. volumes of distilled water rvere added to the still from the 50 ml. graduated

dropping funnel. This procedure lvas continued until 50 ml' of water had

been aclded and 55 mt. of a very faintly yellow distillate had been collected'

The condenser was then detached from the stili-head ancl both arms of the

former were washecl with clistilled I'ater, the u'ashings being collected in a250 ml. Erlcnmeyer flask. The contents of the graduate rvas then quantita-

tivel-v transferred to the same flask and the combined solution was titrated

with standard carbon clioxidc-free 0.020 // sodium hydroxide solution untilthe end-point just began to facle (phcnolphthalein indicator)' The liquor

rvas then brought to a boil to rentove carbou clioxicle, coolcd to room tempera-

ture under the cold lrater tap, and the titration continued until the pink

coloration remained stable for 10 sec. Note r"nas taken of the volume, r, of

stanctrard alkali used. Approrimatel,v 0.5 gm. of sodium bicarbonate rn''as

then added, follou.cd b-v 10 ml. of 1016 sulphuric acid, and, after carbon

dioxidc evoltttion had ccasecl, b1' 1 gm' of potassium iodide' The flask l'as,stoppere<l, shaken, and kept in thc dark for live minutes, after u'hich tirle the

liberatecl iodine lr,as titi-aterl rn ith 0.020 l/ soclium thiosulphate' This

titration,ycc., tvheu multiplied b]'thc empirical factor 1( appropriate 1-o the

particular apparatus anci reagents itt use, gave thc acid equivalent not caused

ty acetic acid. 'fhe acetic acid equivalent u'as therefore (x - Ky) cc' of

0.02 I/ aikali.

Tu,o and one-half hours rvas required for the estimation'

Table I shows that the oxidation quantitatiyel-v recovered the tcrminai

methyl groups in thc first t$ro compounds as acetic acid and is therefore valid

for primarl, clesoxy groups in carbohyclrates. Since the chromic acid oxidation

cloes not clemand the prescnce of an unsubstitutecl 1,2-glycol unit adjacent to

the methyl group, it is certainll' more u'idel-v applicable than the periodate-

oxidation techniquc devclopecl b1' Nicolet ancl Shinn (10)' and is probably

just as convenient. Detcrminations of thc ethylidene group in a sample of

monoethyliclene methl,l-a-glucopyranoside prepared by llill and Hibbert (6),

and of the ethoxl. groups in a technical ethylcellulose, lvere also successful'

The method shoulcl fincl application for group analyses in ethylidcne deriva-

tives of poll,hyclroxy substances and for the estimation of ethoxy in prescnce

of rnethoxl, groups. Anal-vses for acetyl content in the absence of trityl units

agreecl well both n'ith theory ancl with the results of other standard mcthods'

The present proceclure also gave a satisfactor)' result u''ith 6-trityl methyl-a-

"glucopyranoside triacetate.

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+88 c,4i::{D1d.y JIL-R\AL or. RESEAI:H. voL. 25, sEC. a.

]'ABLE I

Acpryr- AND TERMINAL METriyL GRout, ESTTI,TATIoNS

Correctionblank,Ky ml.1

'Total acetyl'Compound Sample,

mgm.

J/ -.')19.9

50 .424.821 .329.149.3(/ 1

70.s

/6 Calc. /s Found

Rhamnose hvdrateIsorhamnose tetraacetateMonoeth I'lidene methyl-a-glucosideEthylcelluloscr2 '

Clucose pentaacetateMcthyl-a-glucoside tetraacetareCellulose aietate36-Trit1'l meth;'l-a-glusoside triacctatea

Tritl'l ss161..e acetate;

0.450.800.360.480. B00.770.600.820.551 .330.81

23.664. 819.626.455 .047 .538.623.023.477.45

l,t.z04.J19.526 .3J.) . t,+1.338.823.623.4t/..)t7 .2

1 Ml. of 0.02 N caustic soda.

. 2 Prese_nted' -by the lrercules Poad.er Co. scmple x 2167-12; oJ zz.6/6 eth.oxy content bysto.ndard alkoryl estimotion.

3 Preseieted by the Eastmon Kod.ah co. An acetone soluble grad.e with 38.6/s acetyl.

..-^4old sample oJ Glodd,ing and. PurtLes (3). M.p. 145" to 147" c. (rncorr.),instead oJ m.p.142" to tr15" C. (corr.).

6 See Table II.TABLE II

AcBryr, coNTENT oF TRITyL cELLULosE AcETATEs

celluloseAcetylated productsl Other

analyses7o Trltyl2 /s Acetyl Moles trityl3 Moles acetyl3

IXIXIXIXI_7

50. 551 .7JI. /49.550.252.3

15.313 .914.518.017.4813.8

0.980.991 .000.991.021 .01

1.671.491 .552.011 .98I.JI

10.719.3, 72.25

14.0, 74.66Q6Q)4

1 Withacet'icanhyd'rid.e,or acetyl chlor'id.e, in pyr'idine for aarious times at aarious telnferotures..2 Analyzed. by Hearon, If,iatt, and Fordyce method (4).3 For calculation see text.a Cramer, Gard,ner, and Puraes melhod. (I ).5 Method. of LIalm, Genung, Williams, and pite (9 ).6 Genung and, Mal.latt method. (Z ).7 Prepared. by Dr. V. R, Grassie.8 See Table I.

Table II summarizes the analyses of a series of acetates derived from threedifferent preparations of ceilulose monotrityl ether. The molar substitutionsper glucose unit of trityl and acetyl were readily calculated from the percentagefigures by means of a simultaneous equation. Since acetylation for various,times in pyridine solution was not likely to affect the trityl unit, the fact that

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LEM I EU X AN D PU RV ES : ou AN T I r AT: M EST I M A',l: ION OF ACET v L AN D OT: HER GROUPS 489

the trityl substitution remained close to the correct value of unity while the

acetyl content varied is good evidence that the analyses for acetyl, as well as

for trityl, are reliable. Other analyses for acetyl, shown to the right of the

table, rvere low.Consideration of the above results, together with those of the previous

investigators (7, 8) shor,vs that the chromic acid oxidation method must be

restricted to terminal methyl groups that oxidize quantitativeiy to acetic

acid. This condition is satisfied when the carbon atom adjacent to the methylgroup is directly linked to at least one oxygen atom, as in CHTCHz-O-,

./CH3CH' , CH3CHOH-, or CHBCOO-. The method fails with corn-

\ 'o-

pounds such as toluene, cellulose propionates and butyrates, in which the

adjacent carbon atom is not substituted by oxygen, because the production of

acetic acid from the terminal methl'l group is not quantitative' Such com-

pounds constitute interfering substances. Interference was also caused by the

allyl ether group' CH2: CH-CHr-O-, which was found by Dr' L' A' Cox

to yield a srnall amount of volatile acid in the chromic acid oxidation.

Acknowledgment

This research rvas partly financed by grants from the National Research

Council of Canada. One of us (R. U. L.) takes this opportunity of thanking

the same organization for two studentships and for sundry maintenance

grants awarded to him.

References

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Abstracted. in Chem' Abstracts, 29 : 1243 ' 1935'

12. Snonvcrx, P. P., Veirsrt.l'N, A. E., and N{e'r'q.novl-ZBMLYANSKAYA' N' N. ^J' -q9l'Ctt""i. U.S.S.R . i :. [iO-,iSS. 1937. Abstracted. in Chem. Abstracts, 31 : 4809. 1937 '

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