Document yrEYNX7VXoee107rqZzbJbQ0d

/ /. t / .auJ^YTICK-L i p U C T I O p OF fal11a ~/f11iL ijJoal)^*"" Graham wdgar and George Calingaert bthyl Gasoline Corporation Laboratory, Yonkers, H. Y. analytical methods have been described for the.determination of tetraethyl lead and related compounds in concentrated prepar ations, and of totraethy 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 co workers 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 ). Let hod 1* TOT. Experimental methods la tijf. rf< CD IfiidiTiULn Caution-- 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 w i t h the hands. (a } 0ravimetrie. reactions: PbLt4 ----- ? IbBrg---- -- ? FbCr04 To about 25cc. of carbon tetrachloride in a 500-cc. Lrlormeyer flask add about^lcc.of tetraethyl lead or its concentrated solution, weighed in a^Lunge pipet (6 )._ Keep the Frlenmeyer 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* 1 deceived fay 2 , 1929 0022252 Gvanorate on a steam bath the carbon tetrachloride from the solid load bromide, To the dry lead bromide add a mixture of 30 cc. of con centrated ammonia (sx>, 2* 0,90) and 50 cc, of oOpercent 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, dilute the filtrate and w swings to 450 ce, and heat to boiling on a hot plate. Bow add slowly and with constant stirring 40 cc. of a 5 percent solution of potassium dichromate, Gtir for 5 minutes while the solution is boiling, then remove from the hot plate and keep in a 'arm place for one hour. Collect the precipitate on a weighed and ig nited Gooch crucible and wash well with hot water. Cry in a crucible air bath, or in an oven at 105 degrees C. and weigh as PbCrOu. (b) Volumetric. ^actions: Fbkt4- ,-bBr 2-- ,>i'blvio04 repare the ammonium acetate solution of load as in section (a), boil it down to 150 cc., and titrate hot with a standard molybdate solution, until al yellow coloration is obtained with tannic acid used as outside indi* eator. The molybdate solution is standardised against a known weight of lead or lead chloride {11). The indicator used is a 0.5 per cent freshly prepare)d solution of tannic acid. Care must be taken always to use the same amount 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. .othod 2 . vaw m iXO s.wAi> i n ij ia U Tw (m; ) (a) Gravimetric. Measure with a pipet lOOcc of gasoline containing tetraethyl lead in a 400-ee beaker, add slowly a solution of 30 per cent bromine in carbon tetrachloride, until the permanent brown-red color of bromine is obtained? Filter promptly through asbestos in a dry Gooch crucible-- or preferably through a fritted Jena glass filter crucible of ho. 2 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. g;r. 1 . 4 0 T i n 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 3cc. Bilute and filter the solution through soft filter paper (if a Gooch crucible was used), rinsing the beaker and crucible with warm water. Just neutralise the filtrate with ammonium hydroxide and add 5 cc. of 50 per cent acetic acid. Con tinue as per Bethod 1 (a). \ Bote 1 -- Gasolines containing a high percentage of unsaturated com pounds absorb bromine vigorously with evolution of heat. In such cases it is highly advisable to dilute the sample with about 10 0 cc. of a volatile petroleum fraction fairly free from unsaturated com pounds (cracked stock), to add the bromine slowly, and to keep the beaker in ice. -hen this precaution is not taken, the results are apt to be low. suitable diluents are, for instance, fighting grade aviation gasoline, petroleum ether, and ligroin. 2This sethod of separating the lead from the gasoline wras -worked out inde- pende ntly in several laboratoris during the early part of the research {3 } lite 2 -- ame gasolines, when treated with bromine, give a tarryliquid insoluble"in gasoline. In such cases the precipitated lead bromide should be ?;ashed 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 (d ). Note 1 -- The molybdate solution may be made to contain 2.380 grams of commercial C. P. salt, in which case 1 ce. of this solution used on an original 10 0 -cc, sample of gasoline corresponds to 0 * 1 cc* of tetraethyl lead (sp.gr. 1.65) per gallon of gasoline. Note 2 -- In some cases the lead nitrate which begins to precip itate when the solution is concentrated to 5 oc, 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 oneration'until a clean white residue of lead nitrate is obtained. . lethod 3. TPTKi.PTHYL Liai IK G0h'C2h'TETSD PBSPARaTI OHS-- Reaction. fb(02II5 )4 / l2 - Pb(C2i%)3l / Ogi%l solutions; 0.1 K iodine containing 50 grams of C.p, potassium iodide per liter; 0.1 IT sodium thiosulfate; starch solution; C.P. benzene. apparatus; 250-cc. glass-stoppered flasks; 'weighing pipet (See Kota 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 M 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 Kr iodine: for a solution its approx imate concentration must be determined by a trial titration.) Ahake vigorously for 2 to 3 minutes.and titrate the excess iodine with 0.1 I) sodium thiosulfate, using starch solution as indicator and shaking vigorously meanwhile. ' The number of cubic centimeters of 0.1 il iodine required times 0.01617 equals the weight of tetraethyl lead in the sample. Note 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. ' K 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 tlie excess iodine is lens than Z ee., the results are usually low and the analysis should be repeated. more than 5 cc. excess can usually be added safely, but Z to 5 cc. is best. If a yellow precipitate (of lead iodide) appears, the analysis should be rejected. bote 4 -- for a convenient type of pipet devised primarily fear this use, see Beferenee (6 ). m e t h o d 4 . -...I .A.Tj.ui'h wi.* u X t a ilX a -l 1 vi 13 jv iliuaLilkilii.l-lYL Guch mixtures are usually obtained in the preparation of alkyl lead compounds by the Grignard reaction. If no other substance is present, the specific 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: PbCCgHgJq / 21 a Pb (G^Hg )51 f O0U5I Ibg (C2II5 }5 / 21 *9 Z TbiGgHgigl The total lead present can be determined by method 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. ethod 5, BIBHYL ihtoD ....LTD, ..ITU OH JL 'VO h.ijj.IaLi Xi.ih*-X) J.K 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 vdth two successive portions of ZQ cc. of a concentrated aqueous ammonia solution. Boll most of the ammonia off gently, acidify the remaining solution vdth nitric acid 1 boil down to about 3 cc., and analyze for lead as per method Z (a) or 2 (b)* ethod 6 . rri.iIvAJ.!iAHTBYL LB YD THIBTHYL LhAD oU*(LTirpuo Extract the preparation vdth ammonia as per .ethod 5 to obtain the triethyl lead compounds. Treat the residue as per method 1 to obtain the tetraethyl lead. E 0022255 (5 ) Ml .ceording to the experience of the authors, i-ethod 1 is as accurate as ordinary analytical methods in inorganic chealotry*** i.e., 0.5 to 0.1 percent dopending on the shill and care applied# in .othod a the accuracy depends somewhat on the concent rati on of lead present, and on the nature of the solvent* (Gasolines con taining largo m o u n t s 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. Method 3 appears to bo good to at least 0*3 per cent ohon pure preparations are handled and when the procedure is followed accurately. The accuracy of method 4 is somewhat unoortain, be cause no alkyl compound of the type rbg&e ha over boon, isolated in the pur state* uonparicon with other properties (density, stab ility) scorns to indicate that th Method is quite reliable# let hod 5 and 6 will :;ive results accurate to within 1 to 2 per cent on the tristhyl load salts# fae accuracy appears to be limited more by the instability of the compounds involved'than by any short comings of the method# :a-lLXu^pii,iyy is stated in the introduction, the methods have been developed primarily for the analysis of' tetraethyl load end accompanying im purities* iae aryl lead compounds are much more etablo~ than the alkyl e x p o u n d s , and the met nods given here would lave to bo mod ified somewhat to apply in their case (8 ). methods 1 and & have been applied successfully to several al kyl lead coMpoimdb beside ethyl# lethods 3 and 4 would probably also be applicable in their case, but th authors have had no exper ience with them# " ;ethods 5 and 6 will determine with certainty th uroeanoo of as little as 1 per cant of a triothyl lead salt in tetraethyl load# Methods 1 and Z appear to be applicable to practically all or ganic solvents, with the exception of those that"`would react too violently or too completely with bromine# ..'.thods 3 and 4. are ob viously applicable only in the absence of substances which react with iodine in the conditions specified* fhe conditions of concentrations and the amount of reagent are of such Importance from the standpoint of accuracy that the method would probably not be applicable to*di lute solutions in the presence of unknown substances* Kg 0022256 (6 ) ACKBOJLBDGic^T The authors wish to acknowledge the assistance of several members of the laboratory staff, particularly 0 , B. Dorion, in carrying out experimental work. HTBBATURK CITED (1) .uborn and Brown, Ind, Eng* Chem., anal. Ed., 1, SO (1929). (2} Birch, J, Inst. Petroleum Tech., 10, 816 (1924). (3) Calingaert, Chem. Rev., 2, 77 (1925). (4) Clark and Smith, J. Phys. Chen., 33, 659 (1929). (5) Cross, Handbook of Petroleum, asphalt, and Natural Gas, p. 711 (1928). (6 ) Edgar, Ind. Eng. Chem., 20, 158 (1928). (7) Berreri, Giorn. chim. ind. applicata, 7, 625 (1925). (8 ) Gilman, J. an Chem. Boc., 50, 1714 (1928) ' (9) Krause, Ber., 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, 8 8 8 , 1282 (1922); Ann., 4-15, 353 (1918). (10) Grmandy, J. Inst. Petroleum Tech., 10, 954 (1924). (11) Treadwell-Hall, "Analytical Chemistry," vol.ll, p. 610, John wiley & Sons, Bew York, 1928. H 0022257