INDUSTRIAL AND ENGINEERING CHEMISTRY
416
Table I .
Absorption of Organic Vapors
Solvent 1:thyl alcohol Acetone E t h y l ether Carbon tetrachloride Benzene Petroleum ether (30-60) E t h y l alcohol lcetone E t h y l ether Carbon tetrarhloride Benzene Petroleum-ether (30-60)
Glycerol 41a. 300 203 60 17
Triethanolamine
Mu. 330 540 136 55 80
1
5
J
GI5 cero1 Base 200 125 40 R
;
Apiezon 11 9
20 160 940
410 300
Vol. 16, No. 6
with those already described. The solvent5 used in making t,hese experiments were chosen to cover a wide range of polarity and no attempt wa3 made to collect) compounds to which glycerol was resistant. The lubrirant is useless with lower alcohol^ and ketones where excellent protection is afforded by the Apiezon 11. It would probably be of value, however, with the higher members of these families where the solubilities in hydrocartmiis become large. The tests described were severe, since the area exposed to the vapor is many times that obt'ained with an ordinary stopcock or ground-glass joint. The effect of fifty liquid solvents on this type of lubricant, has been recorded (4). The absorption result? here are in good agreement. LITERATURE CITED
the thickening agent and their viscosity is consideralily increased. The results of a comparison of the glycerol-base lubricant with a standard commercial stopcock grease, Apieeon 31, are also shown in Table I . The vapors were absorbed here by a 1-gram sample; ot,herwise the experimental conditions were identical
(1) Handbook of Chemistry and Physics, 26th ed., p. 2401, Cleveland. Ohio. Chemical Rubber Publishine Go. (2) Herrington, B. L., and Starr, 31.P., ISD. EN&.CHEM., .\.Is\r> ED.,14, 62 (1942). (3) Iredale, T., Phi2. Mag.. 45, 1097 (1923). (4) Meloche, C. C., and Frederick, IT.G., J . Am. Chem. Soc.. 54, 326.2 I
Determination of Phthalate STERLING B. S M I T H AND J O H N F. STREMPFER Trinity College, Hartford, Conn.
N
I~hIE;ROL7Sternary sy
m i involving pht,halates have been investigated in this laboratory during the past 20 years. The nn:ilytical procedure for the determination of phthalate has irect one, since no direct method known tory in aqueous solution. liappt~lmeier (3) determined phthalates in alkyd resins 1)y the ~irecipitationof potasium phthalate containing one molecule of :ilcohol of crystallization. Thid precipitation is rarried out ill henzc3iic. or in anhydrous almhol-ether solution and is not applicahlt. to aqueous solutions. Fonrobert and Muenrhmeyer ( 2 ) determined phthalate in varnish and Thames ( 4 ) in plasticizers by precipitation of lead phthalate with lead acetate and conversion of this precipitate into lead sulfate which was weighed. Zomhory (6) found that lead could be det'ermined gravimetrically by 1)rccipitation as lead phthalate in alcoholic solution. It was felt that, possibly this procedure could be reversed and phthalate be tletrrmined by adding lead as the precipitating reagent. JYith this t,hought,in mind, this investigation n-as undertaken.
Solubilities of lead phthalate in water and in various concentrations of alcohol were determined at, various temperatures. I t wa3 found that at 25' C. the solubility of lead pht'halate in 335; alcohol b y volume is 2 mg. per 100 cc. of solution. The solubility does not decrease appreciably in higher concentrations of alcohol. Both lead nitrate and lead acetate were independently used as precipitating agents, the former giving low results and the latt'er high results. It is apparent that, when lead nitrate is used as the precipitating agent, nitric acid is one of the by-products. The resulting solution is therefore acidic, accounting for t,he increased solubility of the lead phthalate which is a salt of a weak arid and consequently soluble in a strong acid. An investigation was therefore made t o find the optimum p H for precipitation. A solution made up of lead nitrate and excess sodium phthalate in 33% alcohol by volume as used by Zombory (6),showed a p H of 7.6 using the glass electrode. Determinations were then made using sodium phthalate and a calculated excess of lead nitrate in alcoholic solution of the same strength but with varying acid concentrations. From p H 2.8 t o 6.4 low results were obtained. Above 6.4 high results were obtained.
This is esplained by the solubility of lead phthalate in acid solution and the precipit,ation of lead hydroxide as the alkalinity increahes. This latter fact was substantiated by determining that lead hydroxide starts to precipitate from alcoholic solut'ions rdien the p H reaches 5.1. Rritton (1) found t>hatlead hydroxide come* out of aqueous solution a t a pH of about 6. It is evident that thv optimum pH value a t which phtlialatcs should he determined o w r l a p the pH value a t which lead hydroxide forms. One. caunot hope to make these t,wo error3 self-compensating, since excess lead nitrate ail1 he present in varying amount,s in detcrminnt,ions of phthalates in unkiionn solut.ions. It, .qeemcd that by u4ng lead acetate as the precipitating tigent in place of lead nitrate, the by-product of the reaction would he the weak acetic acid and bett'er results might be obtained. ;1 new difficulty was encountered here, since the precipitat'e came down very finely divided and did not settle out upon standing, rendering filtration and washing virtually impossible. A few determinations were completed by making the pwvipitation in aqueous solution and boiling the mixture before the addition of alcohol. After standing, t,he mixture was wntrifuged and the precipitate rvaqhed and weighed. All the vnlue.; obtained were high and the magnitude of the errors was not ('onsistent. This is believed to be due to the contamination of the precipitate u-ith varying amounts of basic lead acetate. The evidence indicates that. phthalate cannot be determined directly by the addition of lead nitrate or acetate to :tqueou:: solutions containing phthalate ion. LITERATURE CITED
(1) Britton, J . Chem. Soc., 127, 2152 (1925). ( 2 ) Fonrobert and Muenchnieyer, Parbeti-Ztg., 41, 747 (1936). (3) Kappelmeier, Ibid., 40, 1111 (1935). (4) Thames, IND. EKG.CHEM..ASAL. ED.,8 , 418 (1936). (5) Zombory, Magyar Chem. Folydirat, 44, 160 (1938). T H E material for this paper wns taken from a thesis of John F. Streinpier presented t o the Graduate Committee of Trinity College in partial fulfillment of the requirements for the master of science degree.
