Document DG6n4doZ7Kkb1r05bmqaGN9wN

IT O O ro f Crt / / / ahTLYflCi.L ii^tCTIQ&S OF iTfl IWii/T11L -0 Graham wdgar and George Calingaert Lthyl uasoline Corporation Laboratory, Yonkers, K. Y. analytical methods have been described for the.determination of tetraethyl lead and related compounds in concentrated prepar ations, and of tetraethy lead in dilute solution in gasoline* The limits of accuracy of these methods, and their applica bility, under different conditions, have been discussed* The wide distribution of motor gasoline containing tetraethyl lead has stimulated interest in the analytical methods that can be applied to organic lead compounds* -accept for the publications of Krause and his coworkers several years ago (9)~and the more recent article by Gilman (8), practically no methods of analysis applicab3.e to concentrated organic lead preparations have been published. On the other hand, several methods of an alysis of gasoline for tetraethyl lead have been suggested in the literature (1, 2, 4, 5, 7, 10} which, from the authors' experience, are somewhat disk ing in both convenience and accuracy. Since the methods suggested by Krause and by Gilman are of only limited applicability, it may be of interest to present in detail and discuss the methods which have been developed in this laboratory and employed for several years* The methods as described herein apply particularly to tetraethyl lead ana other ethyl lead compounds* Their applicability to other alkyl lead com pounds will be considered in the discussion. for the physical and chemical properties of organic lead compounds on which the analytical : methods are based, the reader is referred to a review of the subject by one of the authors (3). hxperimental methods .ethod 1* TOfnil L.mw.j if Oui iC ifi aiaiiiuTiUh* Taut ion--Concentrated preparat ions of organic lead compounds are highly poisonous. They should be handled under a hood equipped with vigorous suction, and care should be employed to prevent contact with the hands. (a} 0ravimetrie. reactions; PbLth----- ----I:bBrs ---- ? FbCrCd To about 25cc. of carbon tetrachloride in a 500-cc. Lrlonmeyer flask add about^lcc.of tetraethyl lead'or its concentrated solution, weighed in Lunge pipet (6). Keep the Lrlenmeyer flask ice cold, and add slowly and with constant shaking an excess (5 to 10 cc.) of a 30 per cent solution of bromine in carbon tetrachloride* deceived lay 2, 1929 0022252 Jvaporate on a steam bath the carbon tetrachloride from the solid lead bromide. To ti e dry load bromide add a mixture, of 30 cc. of con- centrated ammonia (so, grr.. 0.90) and 50 cc. of SOpercent acetic acid, washing down the sides of the flask. Boil until the precipitate is com** pletely dissolved and any remaining carbon tetrachloride removed. .Fil ter from any insoluble matter and wash the flask out well with hot water into a beaker. Bilute the filtrate and washings to 450 cc, and heat to boiling on a hot plate. Bow add slowly and with constant stirring 40 cc. oi a percent solution of notasaium dichromati ,tir for 5 minutes while the solution is boiling, then remove from the hot plate and keep in a warn place for one hour. Collect the precipitate on a weighed and ig nited Gooch crucible and wash well with hot water. Dry in a crucible air bath, or in an oven at 105 degrees C. and weigh as PbCrOa. {b) Volumetric. 'Reactions: Fbkt4-------- -- y i-bBrS-- >fblvioQ4 Prepare the ammonium acetate solution of lead as in section (a), boil it down to 150 cc., and. titrate hot with a standard molybdate solution, until yellow coloration is obtained with, tannic acid used as outside indi* eator. Tihhee molybdate solution is standardised against a known weight of lead or lead chloride {11). The indicator used is a 0.5 per cent freshly prepared solution of t.aaununAicu acid. Care must be taken always to use the same a: uount of indicator (2 drops) and solution {4 drops), a blank is run on the same amount of water and ammonium acetate, and the amount of molyb date solution used to give a distinct coloration (about 0.3 cc.) is sub tracted from the result of the titration. .ethod 2. ... dii.xj v.umm -Xs u -w aB .l a .eiaUTiL eg { .l .. (a) Gravimetric. Leasure with a pipat lOOcc. of gasoline containing tetraethyl lead in a 400-ce. beaker, add slowly a solution of 30 per cent bromine in carbon tetrachloride, until the permanent brown-red color of bromine is obta nod? Filter promptly through asbestos in a dry Gooch crucible--or preferably through a fritted Jena glass filter crucible of ho. Z porosity--and wash with petroleum ether. Tut the crucible back in the beaker where the pre cipitation was made and add about 3 cc, of nitric acid (sp. gr. 1.40)" in the crucible, ^dd a warm solution of 10 per cent nitric acid in quantity just sufficient to cover the top of the crucible, bring to boiling, re move the crucible, and boil down to about See. Bilute and filter the solution through soft filter paper (if a Gooch crucible was used), rinsing the beaker and crucible with warm water. Just neutralize the filtrate with ammonium hydroxide and add 5 cc. of 50 per cent acetic acid. Con tinue per Tethod 1 (a). Tote 1 -- Gasolines containing a high perejentage of unsaturated com pounds absorb bromine vigorously with evolution of heat. In ouch cases it is highly advisable to dilute the sample with about 100 cc, of a volatile petroleum fraction fairly free from unsaturated corn- pounds n .aa;n cer Ct to (cracked m ice. be low. stock), to add the bromine slowly, and to keep the -hen this precaution i: not taken, the rosiilt are suitable diluents arc. ov instance, fighting grade aviation gasoline, petroleum other, and ligroin. 2Tnis nethod of separating the lead from the gasoline was worked out independe utly in several laboratoris during the early part of the research work on tetraethyl lead, K& 0022253o (5) Mote 2 -- home tgasolines, when treated with bromine, give a tarry liquid insoluble"in gasoline. In such cases the precipitated lead bromide should be washed with special care with petroleum ether, in order to remove the tar thoroughly before dissolving the lead brom ide in nitric acid* (b) Volumetric. Prepare the ammonium acetate solution as in method (2)(a), boil down to 150 cc., and titrate hot with a standard molybdate solution as in method 1(b). Mote 1 -- The molybdate solution may be made to contain 2*380 grams of commercial 0. p. salt, in which case 1 cc* of this solution used on an original 100-cc, sample of gasoline corresponds to 0*1 cc* of tetraethyl load (sp.gr. 1.65) per gallon of gasoline* Mote 2 -- In some cases the lead nitrate which begins to precip itate when the solution is concentrated to 5 cc* volume is contamin ated by a small amount of organic matter. It is then advisable to' evaporate to dryness and treat with fuming nitric acid, repeating the operation'until a clean white residue of lead nitrate is obtain ed. lethod 3. TATRaMTHYL LhaD IK G0h'C^h'TE4TSD PBSPAR^TI OHS-- Reaction. fb(G2H5)4 / lg - Pb(G2H5)3l / OgI%l solutions; 0.1 1 iodine containing 50 grams of C.p. potassium iodide per liter; 0.1 sodium thiosulfate; starch solution; C.P. benzene. apparatus; 250-cc. glass-stoppered flasks; 'weighing pipet (See Note 4) weighing burets or accurate volumetric apparatus. Procedure: weigh accurately 0.5 cc. of pure tetraethyl lead, or 1 cc, or less of its concentrated solution, and add it to 50 cc. of C.P. ben zene in a 250-cc glass-stoppered flask. Add at once 0.1 11 iodine solution in amount equal to 2 to 5 cc. above the theoretical. (For tetraethyl lead the weight of the sample multiplied by 15 gives very nearly the correct volume of 0.1 E iodine; for a solution its approx imate concentration must be determined by a trial titration.) Shake vigorously for 2 to 3 minutes.and titrate the excess iodine with 0.1 M sodium thiosulfate, using starch solution as indicator and shaking vigorously meanwhile. The number of cubic centimeters of 0.1 i! iodine required times 0.01617 equals the weight of tetraethyl lead in the sample. Mote 1 -- In order to obtain accurate results, it is important that the procedure be followed in all its details, especially in regard to the amount of benzene and tbs concentration of pot assium iodide in the iodine solution. 0022254 (4) Mote Z -- hen titrating with sodium thiosulfate part of the iodine is in the aqueous potassium iodide layer and part in the benzene* The titration can be run rapidly until the blue color of the iodine-starch in the water layer disappears. This will reappear on shaking, and the titration is then completed by add ing the thiosulfate drop by drop, shaking well between additions. hots 5 -- If the excess iodine is less than Z ee., the results are usually low and the analysis should be repeated. Lore than 5 cc. excess can usually be added safely, but 2 to 5 cc. Is best. If a yellow precipitate (of lead iodide) appears, the analysis should be rejected. note 4 -- for a convenient type of pipet devised primarily fear this use, see Beference (6). method 4. ITL.TG11IC3 OF S -I JL, 1. .i -> J.i At V '1 T3 in' I lln' nlj iil'ni. l iYLt .n nj^^n>,n^-n--1 Guch mixtures are usually obtained in the preparation of alkyl lead compounds by the Grignard reaction. If no other substance is present, the siDecific gravity will indicate the composition of the mixture, the specific gravity of the two compounds being approximate ly 1.65 and 1.94, respectively. Tore accurate information"will, how ever, be obtained by analysis. Both substances react with iodine: Tb(Gh5)4 / SI a Fb(CH5)SI f C2H5I Fbg(GH5)6 / SI 9 Z The total lead present can be determined by hothod 1. From the results of the iodine titration and the determination of total lead, performed as per methods 1 and 3, the amounts of tetra ethyl lead and dilead hexaethyl can readily be calculated. hethod Th IFTIITL l 1TH OH ;!ThC'UF TBYBnwTHYL LLa D KT The triethyl lead salts are extracted with aqueous ammonia in which they are more soluble than in organic solvents* Irocedure. Dilute about 5 cc, of the concentrated preparation with 20 cc. of petroleum ether, and shake it with two successive portions of 20 cc. of a concentrated aqueous aimionia solution. Boil most of the ammonia off gently, acidify the remaining solution with nitric acid, boil down to about 3 cc., and analyze for lead as per method Z (a) or (b). Lethod 6. HAGTIJYL LlaD THIBTHYL LI l D extract the preparation with ammonia as per i.ethoa 5 to obtain the triethyl lead compounds. Treat the residue as per method 1 to obtain the tetraethyl lead. 0022255 U ^ V/ *>.? 1* 04; 4 >c c u r >oy ceording to the experience of the authors, i-othod 1 is as accurate as ordinary analytical methods in inorganic cheaisfcry-i.o., 0.3 to 0*1 percent depending on the ei-clll and care applied# in . otbod & the accuracy depends somewhat on the concentration of lead present, and on the nature of the solvent* (Gasolines con taining largo amounts of unsaturated compounds tend to give a tarry precipitate, which cannot always bo transferred quantita tively. ) .however, the accuracy of routine analysis is hotter than 1 per cent for quantities of 0.75 to 3*0 ce* of tetraethyl load per gallon of gasoline (0*02 to 0*08 per cent by volume, 0.04 .to 0*16 per cent by weight}, which acorns to be sufficient for all practical purposes* lothod 3 appear to bo good to at least 0*3 per cent when pure preparations arc handled and when the procedure is followed accurately* The accuracy of method 4 is somewhat uncertain, be cause no alkyl compound of the typo rbg&$ Ua over boon isolated in the pur state* comparison with other properties (density, stab ility) seems to indicate that the 1001hod is quite reliable* let hod 5 and 6 will :;ive results accurate to within 1 to 2 per cont on the tristhyl load salts* fhe accuracy appears to be limited more by the instability of the compounds involved'than by any shortcomings of the setlad. is stated in the introduction, the sothods have been developed primarily for the analysis of' tetraethyl load and accompanying im purities. The aryl lead compounds are much sore stable" than the alkyl compounds, and the methods given hers would have to bo mod ified somewhat to apply in their case (8). methods 1 and & have been applied successfully to several al kyl lend compoimdb beside ethyl* iethods 3 and 4 would probably also b applicable in their case, but the authors have had no exper ience with them* lothode Q and 6 will determine with certainty the tsreeesnoo of as little as 1 per cant of a triothyl lead salt in tetraethyl load* methods 1 and Z appear to bo applicable to practically all or ganic solvents, with the exception of those that"would react too violently or too completely with bromine* ethodo 3 and 4. are ob viously applicable only in tho absence of substances which react with iodine in tho conditions specified* The conditions of concent rations and the amount of reagent are of such Importance from the standpoint of accuracy that the nothod would probably not be applicable to*di lute solutions in tho presence of unknown substances* Kg 0022256 (6) AC]^OkIm.DGiA$IT The authors -wish to acknowledge the assistance of several members of the laboratory staff, particularly 0. B. Dorion, in carrying out experimental work. IITBB4TUBB CITED (1) *vbom and Brown, Ind, Bug. Chem., anal. Ed., 1, 2D (1929). (2} Birch, J* Inst. 1 etroleus Tech., 10, 816 (1924). (3) Calingaert, Chem. Bev., 2, 77 (1925). (4) Clark and Smith, J. Phys. Chem., 33, G59 (1929). (5) Cross, Handbook of Petroleum* asphalt, and Natural Gas, p. 711 (1928). (6) Edgar* Ind. Eng. Chem., 20, 158 (1928). (7) Perreri, Giorn. cliim. ind. applicata, 7, 625 (1925). (8) Gilman, J. Am. Chem. Soc., 50, 1714 (1928) (9) Krause, Her., 47, 3257 (1914); 49, 1125, 1415, 1546, 2666 (1916); 50, 202,- 278, 574, (1917); 51 1293 (1918)^52, 150, 2165 (1919); 54, 2060 (1921); 55, 888, 1282 (1922); nnn., 4-15, 353 (1918). (10) Grmandy, J. Inst. Petroleum Tech., 10, 954 (1924). (11) Treadwell-Hall, "Analytical Chemistry," vol.ll, p. 618, John iley & Sons, Get? York, 1928. K 0022257