particles present in the flame with some samples, and these must scatter some light. Such scattering must be small, however, and must be approximately the same for all wavelengths. Absorption by molecular species in the flame has been proved to be the cause of most of the light loss in some cases (5) and is undoubtedly important in others. Other possible causes such as variation of the refractive index within the flame caused by vaporization of salt particles should not be ignored. Continuous
absorption due to ionization of atoms may also contribute. LITERATURE CITED
(1) Allan, J. E., Spectrochim. Acta 18, 259.(1962). (2) Billings, G. K., Atomic Absor tion Newsletter 4, 357, Perkin-Elmer 8orp. (1965). (3) David, D. J., Analyst 86, 730 (1961). (4) Dean, J. A., Carnes, W. J., ANAL. CHEM.34, 192 (1962). (5) Koirtyohann, S. R., Pickett, E. E., Ibzd., 38, 585 (1966).
(6) Van de Hulst H. C., “Light Scattering by Small Partfcles,” Wiley, New York, 1957. (7) Willis, J. B., “Methods of Biochemical Analysis,” David Glick, ed., Vol. 11, Interscience, New York, 1964.
S. R. KOIRTYOHANN E. E. PICKETT De artment of Agricultural 8hemistry University of Missouri Columbia, Mo.
1,2-Dichloroethane as a Solvent for Perchloric Acid-Cata lyzed Acetylation SIR: Ethyl acetate is the traditional solvent for the widely used FritzSchenk (3) perchloric-acid-catalyzed acetylation method for determining organic hydroxyl groups. Their method is also applicable for the determination of amines and mercaptans ( 6 ) , alkoxy(2, 4) and mercaptosilanes ( I ) , and alkoxy- and mercaptogermanes ( 5 ) .
Table 1. Determination of Alcohols, Phenols, and Alkoxysilanes
Per cent of theory” Alcohols and phenols +Butanol 2-blethoxyethanol 2-Propanol Cy clohexanol 2,4-Dimethyl-3-hexamol Phenol 2-tert-Butylphenol 2,6-Diphenylphenol
99.6 f 0 . 7 100.0 f 0 . 1 99.6 f 0 . 4 100.1 f 0 . 6 b 100.4 f 0 . 5 100.4 =t0 . 5 99.9 f 0.9 99.7 f 0 . 4
Alkoxysilanes Diphenyldiethoxysilane 100.1 f 0.8 Dimethyldiisopropoxysilane 99.6 f 0 . 4 7-Octenyltriethoxysilane 100.2 f 0 . 4 2-Pvlethoxy-2-methy1-1thio-2-silacyclopentane” 100.3 f 0.6 1,3-Di-n-propyl1,1,3,3-tetraethoxydisiloxane 99.2 f 0 . 2 7-Chloropropylmethyldiethoxysilane 100.2 iz 0 . 5 Trivinyl-2-met hoxyethoxysilane 99.4 f 0 . 4 a Average and average deviation of tri licate determinations. Acetylation reagent used within 1 hour of its preparation. Reagents mixed, cooled by tap water to room temperature and allowed to stand, with frequent shaking, for about 40 minutes before use. e Bifunctional alkoxy- and mercaptosilane.
1088
ANALYTICAL CHEMISTRY
After testing some 25 lowdielectricconstant solvents, we find that 1,2dichloroethane is superior to ethyl acetate as a solvent in many ways. I n 1,2-dichloroethane, the acetylating agent can be prepared without cooling. Although the newly prepared reagent does become somewhat warm, it may be used within an hour’s time (see footnote b, Table I). [With ethyl acetate, cooling to 5’ C. (3) is necessary during one step of the acetic anhydride-perchloric acid mixing. ] The acetylating agent is virtually colorless, or a very light yellow tint at most. (The reagent in ethyl acetate is yellow to yellow-brown.) Indicator end points are sharp when the yellow color is absent. The acetylating agent has a useful life, a t least two months, that is two or three times longer than reagents in ethyl acetate. Presently, 1,2-dichloroethane is the only solvent besides ethyl acetate in which alkoxysilanes are quantitatively acetylated within 10 minutes. Table I shows typical results for the determinations of alcohols, phenols, and alkoxysilanes in 1,2-dichloroethane. Extensive use of the procedure below has shown that the relative precision (one std. dev.) is about + 0.5% for =SiOC linkages in monomeric or dimeric compounds, f1% for alkoxy-containing poly(dimethylsi1oxane) fluids of 5 to 20 dimethylsiloxy units, and f 2-3% for similar fluids containing trifunctionality high amounts of (RSiOl.5). ACETYLATION METHOD
Acetylating Reagent. Acetic anhydride (1M) in 1,2-dichloroethane (0.15N perchloric acid). Pour 420
ml. of 1,2-dichloroethane into a 500ml. glass-stoppered flask and add 6.2 ml. of 72% perchloric acid and, slowly, while stirring, add 55 ml. of acetic anhydride. Colorless reagents are obtained more consistently in this laboratory if the flasks are first rinsed well with a 1 : l acetic anhydride: 1,2dichloroethane solution. Procedure. Pipet 10 ml. of t h e acetylating reagent into a 125-1111, glass-stoppered flask and add a n accurately weighed 4-5 meq. of a n acetylyzable sample. After a 5minute reaction time, add 35-40 ml. of 6 : 3 : 1 dimethylformamide :pyridine : water hydrolyzing solution. Hydrolyze for 10 to 15 minutes, add 5 drops of 1% thymol blue indicator, and titrate with alcoholic 0.55N potassium hydroxide to the blue end point. Run a n appropriate blank. Dimethylformamide aids in solubilizing both the 1,2-dichloroethane and water. Its presence also sharpens the indicator end point. LITERATURE CITED
(1) Berger, A., Magnuson, J. A., ANAL. CHEM.36, 1156 (1964). (2) Dostal, P., Cermak, J., Novotna, B., Collection Czech. Chem. Commun. 30, 34 f1965). ( 3 ) Fritz,-J. S., Schenk, G. 13., ANAL. CHEM.31, 1808 (1959). (4) Magnuson, J. A., Ibid., 35, 1487 (1963). (5) Magnuson, J. A., Knaub, E. W., Ibid., 37, 1607 (1965). (6) Schenk, G. H., Fritz, J. S., Ibid., 32, 987 (1960). J. A. blAGNCSON R. J. CERRI Silicone Products Department General Electric Co. Waterford, N. Y. Part of a resentation, Division of Analytical C\emistSy, Winter bxeeting, ACS, Phoenix, Ariz., January 1966.
