JULY 1.5, 1940
ASALYTICAL EDITION
Determination of Glycerol in Piesence of Other Organic Compounds The acidimetric method for glycerol has been found very valuable in the determination of glycerol in the presence of a yariety of organic compounds. I t is only necessary that the other compounds do not react n ith periodic acid or if they do react, that no acid is formed.
Examination of Unknown Solutions Solutions known to contain polyalcohols may be examined by oxidizing with periodic acid as described and calculating the results of the acidimetric and iodometric titrations to per cent of glycerol. An acid dichromate oxidation may also be made on the solution and the result calculated to per cent of glycerol. If all three values check, then glycerol is the only material present. If the values are different, a mixture of
387
polyalcohols is indicated and a comparison of the figures obtained will permit some conclusions to be drawn as to the nature of the alcohols.
Literature Cited (1) Fleury, .lfikrochemie, 25, 263 ( 1 9 9 8 ) . (2) Fleury and Boisson, Compt. rend., 204, 1264 ( 1 9 3 7 ) ; 208, 109 (1938). (3) Hann, Maclay. and Hudson, J . Am. Chem. Soc., 61, 2432 (1939). (4) Jackson and Hudson, Ibid., 59, 994. 2049 ( 1 9 3 7 ) ; 61, 959, 1530 (1939). (5) Maclay, Hann, and Hudson, I b i d . , 61, 1660 ( 1 9 3 9 ) . (6) Malaprade, Bull. SOC. chim., (4) 43, 683 ( 1 9 2 8 1 : (5) 1, 8 3 3 (1931). (7) Nicolet and Shinn. J . 4 m . (‘hem. Soc., 61, ltil.5 ( 1 9 3 9 ) . (8) Price and Kroll, I b i d . , 60, 2726 ( 1 9 3 8 ) .
PRESENTED before Section B of t h e Division of Inorganic and Physical Chemistry a t t h e 99th Meeting of t h e American Chemical Society, Cincinnati, Ohio.
Determination of Unsaturation in Aliphatic Hydrocarbon Mixtures by Bromine Absorption J . B. LETIS 4 V D R. B. BRADSTREET, Standard Oil Development Company, Linden,
A modified and time-saving bromidebromate titration for the determination of unsaturates is described. Some sulfur compounds that affect the bromine number have been investigated and catalysts have been found which minimize the harmful effect of these sulfur compounds on the bromine number.
D
URIKG 1929 Buc ( I ) and his co-workers of these labora-
tories investigated the available methods for the determination of the unsaturated content of petroleum fractions. I n order to establish a reference method, they devised a catalytic hydrogenation process by which they were able to evaluate the methods being studied. The method of Francis ( 2 ) was selected as partially meeting the requirements of these workers, inasmuch as it proved excellent for the determination of straight-chain olefins, diisobutylene, and other branched-chain olefins of low molecular weight. They found, however, that a modification of the method was necessary on account of high results obtained, if applied to the determination of highly branched-chain unsaturates and to polymers.
Compounds That Affect Results Buc and co-workers observed that with polymer mixtures the method gave results inordinately high for any purpose. They, therefore, modified the Francis method in the following manner : Introduce into a g. s. flask from 5 to 10 grams of solid potassium bromide, and add the required volume of 0.5 1%’ potassium bromide-bromate as determined by a trial titration, and 20 ml. of 10 per cent (by volume) sulfuric acid saturated with potassium bromide. Allow 3 minutes for liberation of bromine, and then cool the flask and contents in an ice-salt mixture for 10 minutes. Next add the previously cooled sample diluted with chloroform and shake vigorously for exactly 2 minutes. Finally add saturated potassium iodide solution and titrate with standard sodium thiosulfate.
N. J .
The Francis and Buc methods were compared with polybutenes having an average molecular weight of 253. Theoretical determination (from molecular weight) Francis method 1 ml. excess KBr-KBrOa 2 nil. excess KBr-IiBrOa Buc modification 1 ml. excess KBr-EBrOs 2 nil. excess Iionsof the Buc modification. It differs, however, from all these methods in that a trial titration is unnecessary. The excess of potassium bromide-bromate, as shown in Figure 1, inust be kept to a definite minimum. It has not been found necessary to use a cooling medium with the authors' method for determining the bromine number of any of the compounds incorporated in the data of this paper. Table I shows results on several pure compounds, synthet'ic blends made from mixtures of A. S. T. 31. naphtha, nheptane, diisobutylene, and hept'ene-1, and also on a number of saturated compounds. This table shows that the bromine numbers of the pure compounds determined a t 0" C. and a t room temperature are in close agreement with the theoretical calculations. The values obtained on tri- and tetraisobut'ylene show irregularities that have been confirmed by some of t.he aforementioned workers. The bromine numbers of synthetic blends shonm in Table I give further proof that prior cooling is unnecessary. The saturat,ed compounds were run to shox that t,hey do not substitute during the determination.
VOL. 12, NO. i
I.
DETERMINATION OF
Sample Diisobutylene Heptene-1 Trimethylethylene Triisobutylene
.kt Room Temperature
Calculated Values
142.9 162.6 225.2
... ... ... ...
...
Tetraiaobutylene
...
Synthetic Mixtures
... ... ...
1 3
3 4
.1.8 . T . AI. naphtha ,?-Hexane ii-Heotane Isoocltane Methylcyclohexane Tertiary butyl chloride ii-Amyl chloride
T ~ B L11. E
c.
-kt 00
BROMINE NCMBER
EFFECT OF
82.0 83.0
80.0
79.0
76.0
b3.0
82.0 82.0
,..
... ... ...
ISOAXYL LIERCAPTAS OX BROMINE DIISOBUTYLESE
XTJMBER OF
Welght
7*
Bromine KO.a t Room Temperature
Weighr. yo 0.4 0.2 0.1 0.02
Bromine S o . a t Room Temperature 104.8 139.7 144.0
144.0
.4NALYTICAL EDITION
JULY 15, 1940 T.4BLE
111. EFFECTOF
SULFUR COMPOLJSD
Bromine number of diisobutylene = 143 Bromine number of benzyl mercaptan = 67.1 10% by volume benzyl mercaptan is equivalent to 14.11yc
DILUTIOSS IS DIISOBUTYLESE '
(Bromine number of diisobutylene, 143) Concentration, Benzyl 31ercaptan" Isoamyl Disulfidea Volume 5 Sulfur Bromine S o . Bromine S o . com- DiisoRoom Room pound butylene &-eight R temp. Calcd. Weight % temp. Calcd. 126.6 14.11 6.7 132.3 12.47 2 7 10 90 15.3 122.5 111.2 26.9s 24.28 2.6 28 SO 49 64 24.6 105 4 6.2 82.6 40 60 46.09 85.53 56.5 78.1 5 7 33.3 80 20 83.69 100 0 100.00 12 0 , . . 100 00 67 1 .,. C Eastman Kodak Co.. Rochester, X. Y.
TABLE Iv. EFFECT OF
389
CAT.ILYBTS
,On 10'- b y volume solutions of benzyl mercaptan in diisobutylene. 14.11% by u.;ight benzyl mercaptan. Bromine number of diisobutylene, 143) Bromine S o . Catalyst a t Room Temperature 6.7 S o catalyst 86.5 Ammonium molybdate 106.4 Sodium tungstate 110.3 Copper sulfate 53.2 Cobalt chloride 101 1 Sodium arsenate 119 7 Ferric chloride Silver nitrate 121.0 Silver bromide (solid) 129.0 Uranium acetate (saturated solution) 129.0 Uercuric chloride 130 2 Platinic chloride (end point un122 4 certain) Zinc sulfate 129 0
A m y l Mercaptans Bromine S o . Room Weight 5; temp. Calcd. 11 74 11 0 131.9 12 9 124.2 23 04 29.6 109.4 44 39 82 73 .jO 1 83.1 712 ... 100 00
by
Then 67.1 X: 14.11% = 9.46 143 X: 85.8970 = 122.84 Calculated value = 132.30
T h e a p p a r e n t bromine numbers of the other mixtures were calculated in the same manner. From Table IT it can be seen that silver bromide, uranium acetate, mercuric chloride, and zinc sulfate are the most efficient catalysts. Inasmuch as results approaching the calculated value were obtained on a 10 per cent dilution of benzyl mercaptan with the aid of catalysts, it was decided to continue work on this compound along with isoamyl disulfide and amyl mercaptan in concentrations ranging from 10 to 100 per cent. Bromine numbers were determined on five series of mixtures of amyl mercaptan, benzyl mercaptan, and isoamyl disulfide in diisobutylene, using (1) no catalyst, (2) uranium acetate, (3) mercuric chloride, (4) zinc sulfate, and (5) silver bromide. These values are shown in Table V. The data in this table shon7 that the calculated bromine numbers of mixtures of benzyl mercaptan-diisobutylene, isoamyl disulfidediisobutylene, and amyl mercaptan-diisohutylene can be nearly attained by the use of the salts of silver, uranium, mercury, and zinc as catalysts. I t is possible that these catalysts will be helpful in overcoming the inhibitive tendencies of similarly acting compounds which might be found in untreated gasoline. Pure aromatic hydrocarbons had no effect on the bromine number of diisobutylene, either with or without catalysts.
mercaptan, and isoamyl disulfide prevent bromination of diisobutylene and that the bromine numbers found are apparently due to the sulfur compounds themselves. Further investigation was made on a synthetic gasoline (Bromine S o . 79.8) containing saturates, unsaturates, and aromatics to which 20 per cent benzyl mercaptan by volume (27.4 per cent by weight) had been added. The bromine number dropped from 89.4 (Calculated) to 41.1. -4 sample of current gasoline (Bromine S o . 23.4) mixed with 10 Der cent benzvl mercaDtan bv volume (14.06 Der cent by weigh) showed a Ehange i i the bromine number from the Conclusions calculated value of 29.7 to 15.5. With 20 per cent mercaptan by volume (28.1 per cent by weight) the same gasoline was The modified procedure eliminates a trial titrat'ion and the lowered from a calculated value of 35.4 to 26.5. necessit'y for cooling the sample prior to t'itration. A possible explanation for the change in the bromine numThe method as described is applicable to straight-chain oleber of diisobutylene may be taken from the data, which fins, diisobutylene, and other branched-chain olefins of low show that isoamyl disulfide definitely affects this value. Mermolecular weight. With highly branched polymers, the captans, also, influence the determination and it may be asmethod gives erratic results. sumed t'hat since they are easily oxidized to disulfides, t'he Certain sulfur compounds definitely affect the bromine change is due to the presence of these latter compounds. number. At' low concentrations isoamyl mercaptan and a t Furthermore, no method depending upon bromine addition is higher concentrations benzyl mercaptan, amyl mercapt,an, reliable when t'he afore-mentioned types of sulfur compounds are present in appreciable amounts. Since this paper represents preliminary vork, T ~ B Lv. E EFFECTOF C.4T4LYdTS O S BROMIXES U l l B E R O F no attempt has been made to determine the DIISOBUTYLEXE ,Sulfur Compound actual concentration a t which each compound Bromine S u m b e r a t Room Temperature-. Concentration noticeably affects the bromine number. Volume Weight So r r a n i u m Mercuric Zinc Silver
--
?c
Effect of Inorganic Catalysts The obvious need of an agent to counteract the inhibitive effect of certain sulfur compounds led to a search for a suitable catalyst. The determination of the bromine number of a 10 per cent benzyl mercaptan solution in diisobutylene was, therefore, repeated using a number of catalysts as shown in Table IV. One milliliter of a 10 per cent aqueous solution of the c a t a l p t was used with the exception of silver bromide, in which case 0.1 gram of the solid salt was employed. The calculated bromine number of the benzyl mercaptan-diisobutylene mixture is:
Yo
catalyst
acetate
chloride
sulfate
bromide
Calcd.
6.7 15.3 21.6 56.5 67.1
126.8 112 0 101.6
130.1 115.8
124.8
100.5
101.6
128 8 114.5 39.4 38.8 68.1
132 3 122.5 105 4 i8.l
126 ti 111.2
...
123 3 109.5 82 5 13.6 I3 3
...
..
.. , ...
.. ..
181.9 124 2 109.4 83 1
Benzyl Mercaptan 10 14.11 20 40 80 100
26.98 49.64 S5.53 100.00
... ..
...
...
115,s b8.8
66.1
...
Isoamyl Disulfide 10 20 40 80
12.47 24.28 46 09 63.69 100.00
100 .4myl 1Iercaptan' 10 11 74 20 23 04 40 44 39 bo 81 7 3 100 100 00 0 Bromine number of
2 7 2.6 Ci 9
5 7 19 0
111 1 2 70.0 30.7
10s
...
113 8 106.9 io 0 20 4
...
132 8 132 8 123.5 124.7 104 5 104.5 i,j 9 6 6 .i il 2 71.2 diinobutylene ( n e w lot), 140.0. 11 0 12 9 29.6 .50 1 71.2
-
123 3 lot.9 rb.2
13.6
...
...
..
,..
b2 (i
i33.3
...
...
INDUSTRIAL AND ENGINEERING CHEMISTRY
390
and isoamyl disulfide lower the bromine number of diisobutylene. Silver, mercury, zinc, and uranium salts are efficient catalysts for overcoming the deleterious effect of these sulfur compounds. Bromide-bromate methods for unsaturation are when certain types of sulfur compounds are present.
VOL 12, NO. 7
Literature Cited (1)
Buc, H. E., and co-workers, unpublished report, Standard Oil Development Co., September, 1929.
(2) Francis, -4.W., IND. ESG. CHEY.,18, 821 (1926). (3) hlulliken, S. P., and Wakeman, R. L., Ibid., Anal. Ed., 7, 59 (1935). (4) Thomas, C. L., Block, H. S.,and Hoekstra, J., Ibid., 10, 153 (1938).
Determination of Moisture in Native and Processed Cellulose Titrimetric Determination Using Karl Fischer Reagent JOHN MITCHELL, J R . Ammonia Department, E. I. du Pont de Nemours & Co., Inc., Wilmington, Del.
Moisture in various forms of cellulose is determined by cold extraction with methanol followed by direct titration for water with Karl Fischer reagent. The method is simple and precise. Recovery is more nearly complete than by the oven-drying techniques.
T
HE present standard procedures for the determination of moisture in such cellulose products as wood, paper,
cotton, and regenerated cellulose are usually based on weight loss at carefully controlled temperatures. As quantitative methods, however, these analyses are limited to materials containing no other volatile substances. The tentative ,4.S. T. PIT. procedure for moisture in untreated paper, for example, specifies heating to constant weight a t 100" to 105" C. a 6.5-sq. cm. sample of the paper (1). Several modifications of heating technique have been published recently. Gohde (4) described an electrically heated rotary dryer complete with built-in analytical balance and automatic temperature control. Evans and co-workers ( 2 ) outlined a microprocedure involving water evolution followed by absorption in Dehydrite. Tone of these procedures can be considered general, however, because volatile materials other than water either render the methods inaccurate or necessitate empirical corrections. I n the present paper, a simple and efficient cold extraction technique is used in conjunction with a specific titrimetric method for water involving the use of Karl Fischer reagent (3). The reagent consists of a mixture of iodine, pyridine, and sulfur dioxide in methanol solution, and recent work in this laboratory (6) has shown that the following reactions are involved :
and
Reagents Complete instructions for the preparation and standardisation of Karl Fischer reagent have been published (6). [There are a few substances which interfere with the titration for water with Karl Fischer reagent. Reactive aldehydes and ketones react with the methanol to form acetals or ketals and formic acid is dehydrated (6). Boric acid is esterified quantitatively (6).] Dry methanol (
