original concentrations are not equimolecular, the position of the maximum depends on the ratio of the concentrations and the equilibrium constant. It would Seem that those choosing the hethod of continuous variations as a method of attack in this work would do well to examine the purity of the reagents. LITERATURE CITED
(1) Bates, R. G , “Electrometric pH
Determination,” p 117, Wiley, New 1954* (2) Diehl, Harvey, Sealock, R. R.,
Record Chem. Progr. (Kresge-Hooker Sci. Lib.) 13, 10 (1952). (3) Ellingboe, J. L., Ph.D. thesis, Iowa State Ames, Iowa, lg5‘. (4) Harvey, A. E., Komarmy, J. M., Wyatt, G,, A ~ cHEM. ~ ~ 25, . 498
(1953). (5) Job, Paul, Ann. ehim. (Paris) (IO) 9 , 113 (1928). (6) Ibid., (11) 6, 97 (1936). (7) Kinger , W. D., Hume, D. N., J . Am. &em. SOC.71, 2393 (1949). (8) Schwarzenbach, Gerold, “Die kom-
plexometrische Titration,” 2nd ed., p. 30, Ferdinand Enke Verlag, Stuttgart, 1956. (9) Schwarzenbach, Gerold, Biedermann, W., Helv. Chim. Acta 31, 678 (1948). (10) Shriner R. L.,Fuson, R..C., Curtin, D. Y. “gystematic Identification of Organic Compounds,” p. 288, 4th ed., Wiley, New York, 1956. (11) Vosburg, W. C., Cooper, G. R., J . Am. Chem. Soe. 63, 437 (1941) (12) Young, Allen, Sweet, T. R., ANAL. CHEM.27, 418 11955). RECEIVED for review July 11, 1958. Accepted October 14, 1958.
Determination of 2,2-Dichloropropionic Acid, 2-Chloropropionic Acid, and 2,2,3-Trichloropropionic Acid in Chlorinated Propionic Acid by Use of Mercuric Salts ROLAND
P.
MARQUARDT and E. N. LUCE
The Dow Chemical Co., Midland, Mich.
b
Chemical methods were desired to determine 2,2-dichloropropionic acid, 2-chloropropionic acid, and 2,2,3trichloropropionic acid in the amounts usually found in chlorinated propionic acid. By using mercuric salts in the developed analytical procedures, each acid may be determined in the presence of the other acids with a general accuracy to &0.5% of the absolute value.
to pyruvic acid when refluxed with water.
+
CH3CCIzCOOH HzO + CHsCOCOOH
Pyruvic acid reacts with aqueous mercuric nitrate to produce the anhydride of 3,3-bis(hydroxymercuri)-3nitratomercuripyruvic acid. CHsCOCOOH Hg 0
N THE
CHEMICAL REACTIONS USED IN ANALYSIS OF CHLORINATED PROPIONIC ACID
2,2-Dichloropropionic acid hydrolyzes 418
ANALYTICAL CHEMISTRY
+ 3Hg(NOa)2 + HzO
-+
/ \
I
development of Dalapon (2,2dichloropropionic acid), produced by the chlorination of propionic acid, chemical methods of analysis were required. I n addition to a n assay procedure for Dalapon, the main constituent, analytical methods for the chloroand trichloropropionic acids were also desirable. The constituents in a product of this type are best determined directly. Neither direct acidity titrations nor physical methods such as infrared met all the practical requirements. The chemical methods offer a means of determining directly and independently of the other constituents, the chloro-, dichloro-, and trichloropropionic acids in the amounts in which they occur in this product. These procedures depend upon the reactions of these acids with aqueous mercuric nitrate and mercuric propionate solutions.
+ 2HC1 (1)
\ /I
CCOCOOH +5HNOj
(2)
Hg HgN03
The organic mercury compound reacts with aqueous potassium iodide to produce potassium hydroxide (1).
7YCCOCOOH + 12 K I +
0
h?$lgN03
+
3 HzO
+
CH3COCOOK 3KzHgII KNOs 4KOH (3)
+
+
The base is then titrated with standard hydrochloric acid as a measure of the 2,2-dichloropropionic acid. 2-Chloropropionic acid hydrolyzes to lactic acid when refluxed with water.
+
CHsCHClCOOH HzO CH3CHOHCOOH +
+ HC1
(4)
Lactic acid does not react with aqueous mercuric nitrate.
+
CHsCHOHCOOH 4- Hg(NO3)r H 2 0 -P no reaction
(5)
Acidic aqueous dichromate oxidizes lactic acid to pyruvic acid.
+
+
3CH3CHOHCOOH Na2Cr*0, SHY03 + XCHjCOCOOH
+
2Cr(N03)~ 2NaY01
+ i”z0
+
(6)
Then the anhydride of 3,3-bis(hydroxymercuri)-3-ni t r a t o m e r c u r i p y r u v i c acid is produced by Reaction 2 and potassium hydroxide is produced by Reaction 3. The base is titrated with standard hydrochloric acid as a measure of the 2chloropropionic acid. 2,2,3-Trichloropropionic acid reduces mercuric propionate in a boiling aqueous solution, precipitating a mixture of mercurous salts.
+
-+
CHzClCC12COOH Hg(0OCCHzCHs)s ? 4 Hg+acid- (7) The mercurous salt mixture reacts with potassium hydroxide to produce mercurous oxide.
+
2Hg+ acid2KOH + Hg,O 2K+ acid-
+
+ H20
(8)
After the mercurous oxide has been dissolved in dilute acid, the mercury is oxidized and titrated with standard ammonium thiocyanate as a measure of the 2,2,3-trichloropropionicacid. DETERMINATION OF 2,2-DICHLOROPROPIONIC ACID IN CHLORINATED PROPIONIC ACID
Analysis of the product of the reaction between 2,2-dichloropropionic acid and aqueous mercuric nitrate shows that the anhydride of 3,3-bis(hydroxy-
mercuril-3-nitratomercuripyruvic acid is produced: Carbon
HJ-drog~n Nitrogen hlercurv
Found, 70 Theory, $c 4 74 4 71 0 18 1 49 78 31
0 13 1 83 78 68
10.8
11 5
Melting point of the phenylhydrazone of the carbonyl compound produced by decomposition of the organic mercury compound with aqueous potassium iodido is 1Si" C. The literature value for the melting point' of t'he phenylhydrazonc of pyruvic acid is 192" C. From Reactions 1, 2 , and 3, 1 mole of 2,2-dichlorol)ropioiiic acid should give 4 moles of basc. Hon-ever, because Reaction I is not quantitative, the conversion is fixod cywrimcntally a t 91 .770 by propc'r acidity of the solution and propw mncrntrations of both mercuric and cupric. nitrate; 3 moles of 2,2-dichloropropionic wid then produce 11 rnolcs of I)WP('. Apparatus. Erlenmeyer flask, 250ml., connected with a $35/25 balljoint attached to a reflux condenser. I3iichnc.r-type fritted-glass funnel, 60nil. caparity, medium porosity. Filter hell, glass, 11 cm. in outside diameter, 18 cm. high, complete with bottom gnskrt and slide valve. Erlenniqw flask, 250-ml., narrowmouthed. K a s h bottles. Boiling chips. Reagents. ?\leicurie nitrate solution I Tfor chlorinated propionic acid). Dissolve 100.0 granis of yellow mercuric oxide and 60.0 grams of cupric nitrate trihydrate, Cu(S03)2.3H20, in 500.0 nil. of 2.850 + 0.0035 nitric acid nieasurcstl in a volumetric flask. Dilute the solution with water to exactly 1 1itt.r in a \-olumc.tric flask and filter. AIerc*uric. S i t r a t e Solution I1 (for sodium silt of chlorinated propionic acid). I h s o l v e 100.0 grams of yellow mercuric oxide and 60.0 grams of cupric nitrate trihydrate, C U ( S O ~ ) ~ . ~ H in ?O, 500.0 nil. of 3.100 i 0.003S nitric acid measurcd in a volumetric flask. Dilute with water to rxact1)- 1 liter in a volumetric flask and filter. Potassium Iodide Solution. Dissolve 150 granis of potassium iodide in water and dilutci t o 1 liter, make neutral to phenolphthalein indicator, and fill a wash bottle with this solut'ion. IIydrocliloric acid, 0.1 standard solution. Phcnolphtlialein indicator solution. Dissolvc 1.0 gram of phenolphthalein in 80 nil. of 95% ethyl alcohol; dilute with 80 nil. of water. Procedure. CHLoRIsAmD PROPIONIC ACID. Add a weighed sample containing 0.10 t o 0.19 gram of 2,2dichloropropionic acid t o 100 ml. of mercuric nitrate solution I in a balljointcd 250-nil. Erlenmeyer flask. SODICJISALTOF CHLORIKATED PROPIOXIC ACID. Place a weighed sample
containing 0.11 to 0.22 gram of the sodium salt of 2,2-dichloropropionic acid in a ball-jointed 250-ml. Erlenmeyer flask. Add 100 ml. of mercuric nitrate solution 11. Add some boiling chips, attach the flask to the condenser, and reflux the solution for 15 minutes. Cool the flask and contents in a water bath. Using the Buchner-type funnel and the filter brll, filter the precipitate. K a s h the flask and precipitate free of acid with about 50 ml. of water from a Ivash bottle. Discard the filtrate and washings. Place the 250-ml. narrowmouthed Erlcnmeyer flask in the filter bell. Pour 50 ml. of potassium iodide into the ball-jointed Erlenmeyer flask to dissolve any remaining prccipitate. Add this solution to the precipitate in the funnel and stir until the precipitate has dissolved. Apply vacuum and filter the solution containing the dissolved precipitate into the narrow-mouthed Erlenmeyer flask. K a s h the flask and funnel with potassium iodide solution from a wash bottle and add the n-ashings to the filtrate. Place some boiling chips in the flask containing the filtrate and boil the solution for 1 minute. Cool the flask and contents in a v-ater bath. Titrate the solution immediately with 0 . 1 s hydrochloric acid, using phenolphthalein indicator. CALCULATIONS
M I . of 0 . 1 s HC1 X 0.003899 X 100 -
sample o eight 5 2,2-dichloropropionic acid hll. of 0.LY HCI X 0 004499 X 100 sample wight cc sodium salt of 2,2-dichloropropionic acid DISCUSSION
The principal compounds present in chlorinated propionic acid are 2-chloropropionic acid, 2,2-dichloropropionic acid, and 2.2,3-trichloropropionic acid. The sodium salts of these acids are present in the sodium salt of chlorinated propionic acid. As sliown, 2-chloropropionic acid does not form a precipitate Lvith mercuric nitrate solution; 2,2,3-trichloropropionic gives a precipitateof mercurous salts which does not produce a base n hen reacted with potassium iodick solution. Pyruvic acid reacts similarly to 2,2-dichloropropionic acid and if present, must be determined by a separate procedure and a correction applied t o the titration. The factor for pyruvic acid by this method is: ___88.062 - 0.002202 4 x 10,000
Propionic. acid doc>-not interfere. Cupric nitrate has a catalytic effect on the reaction between 2,2-dichloropropionic acid and mer(-uric nitrate in a n acidic aqueous solution, thus helping to fix the reaction a t a certain percentage of conversion.
Because the volume of the reflux solution is critical, carefully measure in a graduated cylinder the amount of mercuric nitrate solution prescribed in the procedure. Long standing of the potassium iodide solution beforehand lessens the titration. DETERMINATION OF 2-CHLOROPROPIONIC ACID IN CHLORINATED PROPIONIC ACID
Analysis of the precipitate obtained in the following analytical procedure for 2-chloropropionic acid shows that the main compound is probably the anhydride of 3,3-bis(hydroxymercuri)-3-nitratopyruvic acid: Found, 52 Theory, % Car ki o n Hydrogen Kitrogen Mercury Oxygen (by difference) Carbonyl as pyruvic acid
4 TB 0 16 0 TO 80 35
4 71 0 13 1 83 78 G8
14 00
14 G5
9 4
11.5
Melting point of phenylhydrazone of the carbonyl compound produced by decomposition of the organic mercury compound with aqueous potassium iodide is 187" C. The literature value for the melting point of the phenylhydrazone of pyruvic acid is 192" C. From Reactions 4,6, 2, and 3, 1 mole of 2-chloropropionic acid should produce 4 moles of base. Honever, because the over-all conversion is not quantitative, it is fixed a t 75% by proper acidity and concentration of the mercuric nitrate solution; 1 mole of 2chloropropionic acid then produces 3 moles of base. Apparatus. I n addition t o t h e apparatus previously listed, t n o dropping bottles, one equipped with dropper t h a t gives large drops, are required. Reagents. Nercuric nitrate solution. Dissolve 45.0 grams of yellow mercuric oxide in 250.0 ml. of 3.100 & 0.003.\- nitric acid measured in a 250ml. volumetric flask. Dilute t h e solution t o exactly 1 liter in a volumetric flask and filter. Sodium dichromate solution. Dissolve 50 grams of sodium dichromate dihydrate, Sa2Cr207.2H20, in water and dilute to 500 ml. Ferrous chloride, saturated solution. Fill a 4-ounce bottle with fwrous chloride tctrahydrate crystals. FeCl2.4H20. Add water containing 5 ml. of concentrated nitric acid per liter and shake the bottle periodically until the solution is saturated with ferrous chloride. Pour some of the solution into a dropping bottle equipped with a dropper that gives large drops. n-Octyl alcohol in a dropping bottle. Potassium iodide solution. Dissolve 150 grams of potassium iodide in water and dilute the solution to 1 liter. RIake neutral to phenolphthalein indicator. VOL. 31, NO. 3, MARCH 1959
419
Hydrochloric acid, 0.1N standard solution. Phenolphthalein indicator solution prepared as described. Procedure. CHLORINATEDPROPIONIC ACID. Add a weighed sample of chlorinated propionic acid containing 0.00 to 0.040 gram of 2-chloropropionic acid (0.18 gram maximum sample size) to 100 ml. of mercuric nitrate solution in a ball-jointed 250-ml. Erlenmeyer flask. SODIUM SALT OF 2-CHLOROPROPIONIC ACID. Place a weighed sample containing 0.00 to 0.048 gram of the sodium salt of 2-chloropropionic acid (0.20 gram maximum sample size) in a balljointed 250-ml. Erlenmeyer flask. Add 100 ml. of mercuric nitrate solution. Add some boiling chips, attach the flask to the condenser, and reflux the solution for 15 minutes. Cool the flask and contents in a water bath. Using the Biichner-type funnel and the filter bell, filter the precipitate, placing the filtrate in another balljointed 250-ml. Erlenmeyer flask. Wash the precipitate with three 10.0-ml. portions of water and add the washings to the filtrate. Discard the precipitate and clean the funnel. Add 2.0 ml. of sodium dichromate solution to the filtrate; swirl the filtrate and let stand for 5 minutes. Reduce the excess dichromate by the dropwise addition of saturated ferrous chloride solution (the end point will be indicated by a blue-green with the absence of yellow background). Then add 5 additional drops of ferrous chloride solution, 2 drops of n-octyl alcohol, and some boiling chips. Attach the flask to the reflux condenser and reflux the contents for 15 =t1 minutes. Cool the flask and contents in a water bath. Using the Buchner-type funnel and the filter bell, filter the precipitate and wash it and the flask well with water. Discard the filtrate and washings. Place a 250-ml. narrow-mouthed Erlenmeyer flask in the filter bell. Pour 50 ml. of potassium iodide solution into the ball-jointed Erlenmeyer flask to dissolve any remaining precipitate. Add this solution to the precipitate in the funnel and stir until the precipitate has dissolved. Apply vacuum and filter the solution containing the dissolved precipitate into the narrowmouthed Erlenmeyer flask. Wash the flask and funnel with potassium iodide solution from a wash bottle, adding the washings to the filtrate. Place some boiling chips in the narrow-mouthed Erlenmeyer flask and boil the filtrate for 1 minute. Cool the flask and contents in a water bath. Titrate the solution immediately with 0.1N hydrochloric acid, using phenolphthalein indicator. CALCULATIONS
M1. of 0.1N HCl X 0.003618 X 100 sample weight yo 2-chloropropionic acid M1. of 0.1N HC1 X 0.004351 X 100 sample weight yosodium salt of 2-chloropropionic acid
420 *
ANALYTICAL CHEMISTRY
DISCUSSION
Both 2,2-dichloropropionic and 2,2,3trichloropropionic acids produce precipitates when reacted with mercuric nitrate solution; because these precipitates are filtered before the precipitate from 2-chloropropionic acid is developed, interference with the determination of 2-chloropropionic acid is eliminated. Pyruvic acid, if present, reacts similarly to 2,2-dichloropropionic acid and does not interfere rTith the determination, nor does propionic acid. Acrylic or chloroacrglic acids would interfere. Results will be low if the titration is much greater than 10 ml. of 0.1N hydrochloric acid. The sample taken for analysis should contain less than 0.040 gram of 2-chloropropionic acid. Also, the maximum sample size is limited to about 0.20 gram because excessive amounts of 2,2-dichloropropionic acid and 2,2,3-trichloropropionic acid will react with enough mercuric nitrate to influence the results for 2-chloropropionic acid. Because the volumes of the two reflux solutions are critical, the amounts of mercuric nitrate solution and of water prescribed in the procedure should be carefully measured in suitable graduated cylinders. The reflux time prescribed for the development of the precipitate by the reaction of mercuric nitrate with the product from 2-chloropropionic acid should be followed closely. Long standing of the potassium iodide solution beforehand lessens the titration. DETERMINATION OF 2,2,3-TRICHLOROPROPIONIC ACID IN CHLORINATED PROPIONIC ACID
The reduction when aqueous mercuric propionate reacts with 2,2,3-trichloropropionic acid produces a precipitate consisting of a mixture of mercurous salts. Perhaps the main product is the mercurous salt of monochloropyruvic acid. Analysis of the product gave :
% Carbon Hydrogen Chlorine Nitrogen Mercury
Oxygen (by difference)
8 38 0 63
7 0 62 20
0
61
86 5
Reaction of the product with aqueous potassium hydroxide immediately gives a black precipitate of mercurous oxide. With proper concentration and acidity of the mercuric propionate reagent, 3 moles of 2,2,3-trichloropropionic acid produce enough precipitated mercurous salts to give, after oxidation, 7 equivalents of mercuric mercury. Apparatus. I n addition to the apparatus listed, a Buchner-type frittedglass funnel, 60-ml. capacity, fine porosity, is necessary.
Reagents. Mercuric propionate solution. Dissolve 100.0 grams of yellow mercuric oxide in 500.0 ml. of 2.500 rt 0.003N nitric acid measured in a volumetric flask. Dissolve 75.0 grams of sodium propionate in the solution. Dilute the final solution with water to exactly 1 liter in a volunietric flask and filter. Methanol, technical grade. Methanol-water solution. Dissolve 1 volume of water in 2 volumes of methanol. Fill a wash bottle with this solution. Potassium hydroxide, 1N solution. Fill a wash bottle with some of this solution. Potassium iodide solution. Dissolve 200 grams of potassium iodide in water and dilute to 500 ml. Nitric acid, concentrated. Potassium permanganate, aqueous solution. Dissolve 25 grams of potassium permanganate in water and dilute the solution to 500 ml. Fill a dropping bottle with this solution. Hydrogen peroxide, 30% (Super0x01). Fill a dropping bottle with this reagent. Ammonium thiocyanate, 0.1N standard solution. Ferric ammonium sulfate, indicator solution. Dissolve 100 grams of ferric ammonium sulfate, Fez(SO&. (NH4)zSO4.24H20in 100 ml. of water. Acidify the solution with 15 ml. of concentrated nitric acid. Procedure. Add a weighed sample containing not over 0.38 gram of 2,2,3-trichloropropionic acid to 50.0 ml. of mercuric propionate solution in a 250-ml. ball-jointed Erlenmeyer flask (for the sodium salt of Dalapon, the sample may be added to the Erlenmeyer flask prior to addition of the mercuric nitrate solution). Add some boiling chips, attach the flask to the condenser, and reflux the solution for 5.0 minutes rt 15 seconds. Cool the flask and contents in a water bath and add 100 ml. of methanol. Using the Buchner-type funnel and the filter bell, filter the precipitate. Wash the Erlenmeyer flask and precipitate with methanol-water solution from a wash bottle. Discard the filtrate and washings. Pour 50 ml. of 0.1N potassium hydroxide into the Erlenmeyer flask and let the basic solution react with any remaining precipitate. Pour the solution on the precipitate in the funnel; stir the mixture periodically for 10 minutes to ensure that all the precipitate reacts with the potassium hydroxide. Add 10 ml. of potassium iodide solution to the basic mixture in the funnel and stir for 1 minute. Filter the mercurous oxide, washing the flask and funnel well with 0.1N potassium hydroxide from a wash bottle until no iodide remains. Discard the filtrate and washings. Place a 250-ml. narrow-mouthed Erlenmeyer flask in the filter bell. Dissolve the residual mercurous oxide in the ball-jointed flask with 3.0 ml. of concentrated nitric acid. Pour the acid on the mercurous oxide in the Buchnertype funnel and stir until all of the mer-
curous oxide dissolves. Filtcr the acid solution into the narrowmouthed Erlenmeyer flask. Repeat with 2.0 ml. of concentrated nitric acid. Wash the funnel and flask with water until the filtrate totals about 50 ml. Add potassium permanganate solution dropwise to the filtrate until the filtrate remains a deep purple. Let stand for 5 minutes. Then add 30% hydrogen peroxide dropwise to the solution until the color from the excess potassium permanganate disappears. Cool the flask and contents in a water bath. iidd 2.0 ml. of ferric ammonium sulfate indicator solution and titrate the filtrate with 0.LY ammonium thiocyanate solution. CALCULATIONS
111. of 0 1 S SHdCNS X 0.007601 X 100
Table I.
Known 1
Analysis of Known Solutions Containing 2-Chloropropionic, Dichloropropionic, and 2,2,3-Trichloropropionic Acids
Chloropropionic Acid, yo Calcd. Found 3 3
2
6.4
3
33 9
4
5 3
5
0.8
2,2-Dichloropropionic Acid, Calcd. Found
3 9 3 5 3 4 6.8 6.8 7.0 34 2 34 4 34 0 5 9 55 5 4 0 6 0.5 0 5
92 6 87.2 57 5 64 5 37.1
92 2 92 3 92 3 87.1 86.6 86.8 57 1 56 9 56 9 63 3 63 1 63 2 35 0 35 0 34 5
2,2-
2,2,3-Trichloropropionic Acid, yo Calcd. Found 4 0 45 6.4 8 6
30 2 62 1
4 3 4 1 6.7 7.0 6.8 8 9 9 0 9.1 30 6 30 7 30 7 62 9 6.7 4 62 8
sample weight =
7c2,2,3-trichloropropionic acid
111 of 0.1-V XHaCSS X 0.008546 X 100
sample weight yo sodium salt of 2,2,3-trichloropropionic acid
=
DISCUSSION
The principal conipounds present with 2,2,3-trichloropropionic acid are 2chloropropionic acid and 2,2-dichloropropionic acid. 2-Chloropropionic acid does not form a precipitate with mercuric propionate solution. 2,2-Dichloropropionic acid produces a precipitate with mercuric propionate solution which is probably the anhydride of 3,3-bis(hydroxymercuri)- 3- propionoxymercuripyr w i c acid; this organic mercury compound dissolves in an aqueous solution of potassium hydroxide and potassium iodide Kithout the forniation of mer( urous oxide. Pyruvic acid reacts like 2.2-dichloropropionic acid. Propionic :wid does not interfere. Because the volume of thc refluv soltion is critical, the amount of mercuric propionate solution prescribed in the procedure should be carefully measured in a graduated cylinder. For best results, the reflux time prescribed for the development of the precipitate by the reaction of mercuric propionate with 2,2,3-trichloropropionic arid should be followed exactly. ANALYTICAL DATA
Pure samples of 2,2-dichloropropionic acid, 2-chloropropionic acid, and 2,2,3trichloropropionic acid upon which to base the standardization of the respective mercuric salt solutions for the analysis of these compounds n-ere difficult to prepare. A small amount of 2,2-dichloropropionic acid was purified by recrystalliza-
tion and assayed 99.7% by the freezing point method. The above procedure gave assays of 99.5, 99.9, and 99.4%. -4 purified pample of 2-chloropropionic acid n-as obtained by fractional distillation. The sample contained 32.02% chlorine, which calculated to 98.0% 2-chloropropionic acid. Infrared analysis s h o m d very little impurity present. Analysis by the above analytical procedure for 2-chloropropionic acid gave assays of 97.7, 98.7, and 97.5%, averaging 98.0%. The other procedures showed 2.3% 2,2-dichloropropionic acid, and 0.3% 2,2,3-trichloropropionic acid. A sample considered to contain 98.0% 2,2,3-trichloropropionicacid was prepared. The probable impurities were chloroacrylic acid and 2,2-dichloropropionic acid. Analysis by the above analytical procedure for 2,2,3-trichloropropionic acid gare assays of 97.3, 97.1, 98.1, and 97.9%, averaging 97.6%. The other procedures showed 1.1% 2chloropropionic acid and 0.4% 2,2-dichloropropionic acid. The figure for 2chloropropionic acid was surprising and was probably due to chloroacrylic acid. A sample of 2,2-dichloropropionic acid obtained by fractional distillation was analyzed by these procedures and found to contain 99.1% 2,2-dichloropropionic acid, 0.3y0 2-chloropropionic acid. and 0.7% 2,2,3-trichloropropionic acid This sample and the aforementioned samples of 2-chloropropionic acid and 2,2,3-trichloropropionic acid were used as stock samples to prepare a series of known solutions. The compositions of the knonn solutions were calculated from the anal! tical data obtained on each stock sample. The analytical data obtained by the three procedures on the known solutions are tabulated in Table I. The low figures found for 2,2-dichloropropionic acid
in knon-ns 4 and 5 are believed to be caused by the stronger acidity which the large amounts of 2,2,3-trichloropropionic acid gave to the refluu solution for the precipitation of the nnhydride of 3,3-bis (hydroxymercuri)- 3 -nitratomerruripyruvic acid. Homver, the samples of chlorinated propionic acid analyzed never exceeded 10% 2,2,3-trichloropropionic acid. The mercuric nitrate solution for 2,2dichloropropionic acid gave high results when applied to the sodium salt of the sample. This was thought to be caused by the decreased acidity of the reflux solution for the precipitation of the anhydride of the 3,3-bis(hydroxymercuri)-3-nitratomercuripyru~-icacid. To standardize the mercuric nitrate solution for the analysis of the sodium salt of 2,2-dichloropropionic acid, a n anhydrous standard sample closely approximating the commercial samples ITere prepared. It was calculated to contain 90.3% of the sodium salt. Analysis by the above analytical procedure for the sodium salt of 2,2-dichloropropionic acid gave assays of 90.1, 90.5, and 90.1%. A sample calculated to contain 98.0% of the sodium salt of 2-chloropropionic acid was prepared. Analysis by the analytical procedure for 2-chloropropionic acid gave 98.7, 96.9, and 97.9%. A pure sample of the sodium salt of 2,2,3-trichloropropionic acid could not be prepared because of decomposition of the compound. LITERATURE CITED
(1) Whitmore, F. C., “Organic Compounds of Mercury,” pp. 73-5, Chemical Catalog Co., New York, 1921.
RECEIVEDfor review March 18, 1958. Accepted September 16, 1958.
VOL. 31, NO. 3, MARCH 1959
421
