January 15, 1932
IIC’DUSTRIAL A N D E N G I N E E R I N G
F , Snap button ~ p r i n g - ~ / ~inch ~ in diameter, 1 inch long; fine steel compression spring. G, Finger rests-make two; bent from S/winch iron rod; ends screwed into barrel.
CHEMISTRY
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back of razor ground to fit groove in cutter head; blade snapped off or ground to proper length ( 7 / ~ inch) after back has been sawed through. The reproducibility of the weights of the sodium pellets obtained is even better than that originally required. For example, with the stop set to cut a 200-mg. pellet, twelve successive units were cut from a freshly pressed rod of sodium 5 mm. in diameter. These were allowed to fall into dry benzene, later individually removed, dried quickly, and weighed on an analytical balance sensitive to 0.1 mg. Of the twelve pellets, eight weighed exactly 200 mg., two weighed 199 mg., one 201 mg., and one 202 mg. When used as described, the operation is so rapid that the amount of oxidation is negligible and the purity of the resultant units is simply the purity of the original metal. Since far more oxidation obviously occurs when the sodium pellet is heated prior to the addition of the organic compound in the test for elements than takes place in its preparation, a more detailed determination of the actual sodium content was deemed unnecessary. ACKNOWLEDGMENT
FIGURE 3. ASSEMBLYOF CUTTER
SODIUM
PI, Sodium feed tube-preferably of stainless steel or of nickel. I , Plunger return spring-steel compression spring, inch in diameter, 23/8 inches long; wire 0.047 inch in diameter.
J,Cap screw--l/q inch in diameter, ‘/e inch long; fillister head. K , Set screws-make two, inch in diameter; flat point. L, Set screw--’/s inch in diameter; flat point. M, 8top--a/le inch in diameter, 8/4 inch long; make fine thread for close adjustment. N , Lock nut-threaded for stop screw M . 0, Snap button upper hearing--a/l~ inch in diameter; cut groove in upper face to aid in screwing in. P , Cutter blade-safety-razor blade of Gem or Eveready type;
The authors wish to thank A. A. Morton, V. F. Harrington, C. L. Gallagher, and I. S. Cliff for invaluable suggestions and criticisms. LITERATURE CITED Gattermann, “Practical Methods of Organic Chemistry,” 3rd American from 11th German ed., pp. 385-6, Macmillan, 1921. (2) Mulliken and Gabriel, 8th. Intern. Cong. Appl. Chem., 6, 208-11 (1)
( 1912). (3) Parke, J. Chem. Education, 4, 918-19 (1927). RECEIVPD June 5 , 1931. Contribution 73 from the Research Laboratory of Organic Chemistry, Massaohusetts Institute of Technology.
Determination of Tetraethyl Lead in Ethyl Gasoline E. L. BALDESCHWIELER, Standard Oil Derelopment Company, Elizabeth, N . J .
A
S MEIiTIOXED by A S I M P L E and reliable gravimetric method PROCEDURE E d g a r and Calingaert for the determination of tetraethyl lead in gasoline The method d e p e n d s upon (2), the various methand other petroleum products is described. the fact that t e t r a e t h y l lead ods published in the literature f o r t h e d e t e r m i n a t i o n of The method has been in for several Years in is completely decomposed by this laboratory and has given complete satisshaking the gasoline s o l u t i o n tetraethyl lead are either too with concentrated nitric acid, tedious or are l a c k i n g in acfaction. It is specially adapted for intermittent curacy. The bromine method work and requires only ordinary laboratory fprming l e a d n i t r a t e . The liquid separates into two layers published by Edgar and technic. Its use in the analysis of other organoand the lower layer, containgaert (2) is rapid and accurate but sometimes troublesome, esmetallic compounds is discussed. ing the acid with most of the lead n i t r a t e , can be drawn pecially with gasolines rich in unsaturated compounds which require the addition of a large off. Since lead nitrate is not very soluble in concentrated amount of bromine. This results in the evolution of much nitric acid, the acid shaking is followed by washing in water hydrobromic acid and, sometimes the formation of gummy in order to remove the last traces of lead nitrate. The reprecipitates which are difficult to handle, and it is the writer’s action takes place without appreciable rise in temperature, experience that unless special precautions are taken, low re- even with gasolines rich in unsaturated compounds, and can therefore be safely carried out in a separatory funnel, sults are obtained. To obviate these inconveniences, the method described using the method described below. Measure 200 cc. of the gasoline into a 500-cc. glass-stopherein has been devised and used in this laboratory for sevpered separatory funnel. Add 20 cc. of concentrated nitric eral years.
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acid and shake for 15 minutes. Loosen the stopper carefully and let stand 2 minutes. The acid layer readily separates a t the bottom of the funnel. I n the case of some highly cracked gasolines, dark-colored compounds are sometimes formed which may obscure the line of demarcation of the two layers. This can be obviated by washing the sides of the funnel with 3 or 4 cc. of distilled water from a wash bottle. Run the acid layer into a 200-cc. plain Pyrex beaker and set aside. Add 20 cc. of water to the funnel and shake 15 minutes. Let stand 2 minutes and draw off the lower water layer into the beaker containing the acid solution, Repeat the acid and water shaking described above, collecting the acid and water layers in the original beaker. Any emulsion which may be formed between layers and which may contain some lead is drawn off with the aqueous portion, as the small amount of organic matter which is carried along will be destroyed in the subsequent procedure. The collected acid and water portions, which should amount to about 80 cc., are rapidly evaporated on a hot plate to a volume of 20 cc. Cool and add carefully 15 cc. of concentrated sulfuric acid; cover the beaker with a^ watch glass tilted with a glass hook and boil rapidly until fumes of sulfur trioxide are observed. The presence of organic matter will color the solution black, owing to the charring action of the sulfuric acid. This organic matter will be destroyed very rapidly by adding one or two drops of concentrated nitric acid (a) to the boiling solution. The reaction is very violent, but no mechanical loss should occur if the acid is added to the side of the beaker and the latter kept well covered. Continue boiling, adding nitric acid from time to time until the organic matter is all destroyed and the solution is colorless. This operation should take about 20 minutes. Cool, add carefully 20 to 25 cc. of water, stir well, and evaporate again until fumes of sulfur trioxide (6) are given off. Dilute with cold water, making the total volume up to 150 cc. Cool in ice water (c) for 1 hour and filter through an ignited and weighed Gooch crucible. Wash several times with 2 per cent sulfuric acid and finally twice with 10 cc. of 95 per cent alcohol. Dry, ignite, and weigh as lead sulfate. The amount of tetraethyl lead per gallon is calculated as follows: grams of lead sulfate per cc. of sample times the factor 2445 equals the number of cc. of tetraethyl lead per gallon. In calculating the factor 2445, the specific gravity of tetraethyl lead is taken as 1.65. This method has been checked against the bromine precipitation method (2) on the same sample of ethyl gasoline. The results, given in Table I, show excellent agreement. TABLE I. ANALYSISOF ETHYL GASOLINE TBTRAETHYL LEADCONTENT Cc./gal. Cc./gal. CcJgal. A 3.10 3.10 Av. 3.10 B 3.09 3.10 Av. 3.10 C 3.13 3.14 Av. 3.14 lead weighed aa lead sulfate. A, nitric acid extraction method. B bromine precipitation method; lead weighed as lead chromate. recipitation method; lead determined volumetrioally with C: bromine ammonium moyybdate. METHOD USED
Vol. 4, No. 1
(6) The second evaporation is generally necessary, since concentrated sulfuric acid sometimes holds nitric oxides rather tenaciously. The presence of these oxides tends to give low results b increasing the solubility of lead sulfate. (c) dooling 1 hour in ice water or letting stand overnight gave the same results. Slightly lower results were obtained on filtering after standing 3 hours at room temperature.
TIMEREQUIRED The time required for a tetraethyl lead determination by the nitric acid extraction method is about 4 hours. The shaking operation described in the first part of the method can be done by hand when only one sample is being analyzed. For routine work, many determinations can be made simultaneously by using a suitable shaking machine capable of accommodating a number of separatory funnels. The time required for complete decomposition and extraction has been determined by the following experiment: A solution of tetraethyl lead in gasoline was made up to contain about 3.0 cc. of tetraethyl lead per gallon. Several samples of this solution were analyzed as described in the method, except that the shaking was carried on for various lengths of time. The results are given in Table 11. TABLE11. TIMENECESSARY FOR COMPLETE EXTRACTION OF Pb(C*H&FROM GASOLINE TIMEOF SHAKINQ Min.
Pb(CsH& EXTRACTED Cc./gal. 2.09 3.16 3.20 3.27 3.27
Another experiment showed that a single nitric acid treatment for 30 minutes followed by alwater shaking for the same length of time removed only 98 per cent of the tetraethyl lead. The results of the above experiments indicate that the minimum shaking time is 12 minutes and that the operation must be repeated for the complete extraction of the lead.
FURTHER APPLICATIONS Many other organo-metallic compounds soluble in gasoline can be decomposed and the metal extracted with nitric acid by the method just described. This has been used, for instance, in the determination of bismuth, iron, and zinc compounds as well as for the decomposition of many metallic soaps present in compounded oils. When the metallic compounds are dissolved in a heavier petroleum fraction, such as gas oil or lubricating oils, the sample is diluted with a gasoline free from unsaturates and the extraction carried out as described. The process outlined for destroying the organic matter is useful in the analysis of organic compounds containing such elements as lead, mercury, or antimony, which are too volatile to be estimated by ashing the sample. If the material is not soluble in gasoline, the sample can be treated directly with nitric acid, fumed with sulfuric acid, and the organic matter destroyed with nitric acid, as previously described. The metal is thus obtained in a sulfuric acid solution from which it can be determined by the usual analytical methods.
The accuracy of the method is within 0.02 cc. of tetraethyl lead per gallon; the results obtained by this laboratory have always agreed with those of the Ethyl Gasoline Corporation's laboratories using the bromine volumetric method.
ACKNOWLEDGNENT The author wishes to acknowledge the assistance of H. C. DeHoff in carrying out the experimental work.
NOTES. (a) Birch (1) uses potassium nitrate for the oxidation of the organic matter. This was tried, but low results were obtained, probably owing t o increased solubility of lead sulfate in the presence of potassium sulfate. Oxidation of the organic
(1) Birch, J. Inst. Petroleum Tech., 10, 816 (1924). (2) Edgar and Calingaert, IND.ENQ.CHEIM., Anal. Ed., 1, 4 (1929).
matter proceeds much faster with nitric acid than with potassium nitrate.
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LITERATURE CITED
RECEIVED July 28, 1931.
