Qualitative Analysis of Organosilicon Compounds and Polymers Determination of Hydrocarbon Substituents CII.iRLES 1.BURKHARD AND FRANCIS J. NORTON, General Electric Co., Schenectady, N .
HEN the presence of silicon is established in an organic
compound, the usual methods of organic qualitative analy-
sis generally are insufficient to give adequate clues as to the oossible identitv and structure of the unknown compound, mixture, or polymer. Unlike acids, esters, and amines, the typical organosilicon compounds do not form solid class derivatives. It therefore becomes necessary to develop a scheme Of qualitative analysis for this class of compounds. This paper reports a method of establishing the identity of the monovalent hydrocarbon radicals attached directly to silicon. KiPPing ( 2 ) has observed that the Silicon-PhenYl bond is cleaved by acids to give benzene. This is a general reaction enabling one to cleave both aryl and alkyl groups from silicon.
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mass spectrometer. I t is possible to detect hydrogen and methane in the presence of air. AS only these two materials have sufficient vapor pressure to appear with the air when the sample is at liquid nitrogen temperature, about -195" c., it is possible to detect these compounds readily in the presence of the higher hydrocarbons. After the presence or absence of hydrogen and methane has been established, the sample bulb is pumped to pressure of micron or less while still being cooled by liquid nitrogen. When the pumping has been completed the sample is closed off, the liquid nitrogen is taken away, and the sample bulb is allowed t o warm to room temperature. By this procedure, the methane, hydrogen, and components of air are completely eliminated from the sample bulb. The higher boiling hydrocarbons are then determined. Water will appear in the spectrum, as masses 16, 17, and 18, but it does not interfere. Total time consumed is about 15 to 30 minutes per sample. ~
The following radicals have been identified in organosilicon compounds: hydrogen, methyl, ethyl, butyl, amyl, cyclohexyl, and phenyl. I t is possible by this technique to differentiate between the silicon-hydrogen bond and the silicon-silicon bond. Both bonds are hydrolyzed by alkali to give hydrogen, but only the siliconhydrogen bond reacts with acid to give hydrogen. In molecules where it is suspected that both silicon-hydrogen and siliconsilicon bonds are present, quantitative analysis data can be used simultaneously to confirm the presence of the silicon-silicon bond.
The hydrocarbon is identified by means of the General Electric mass spectrometer. I t has been possible to recover as much as 707, of the total available methane from a polydimethyl siloxane polymer.
A 10- to 500-mg. sample of the unknown organosilicon compound is digested by heating with 10 to 15 ml. of concentrated (95%) sulfuric acid. The gaseous reaction products are collected in a gas buret and washed with aqueous sodium hydroxide to remove the carbon dioxide and sulfur dioxide. The gas sample, which is diluted with air, is then transferred to an evacuated bulb and placed in the sample train of the mass spectrometer. The entire sample is cooled with liquid nitrogen. After sufficient time has elapsed to cool the entire sample bulb thoroughly, a small sample of the gas, noncondensable by liquid nitrogen, is bled into the sample train. This small aliquot is allowed to enter into the sample system, then to flow through a calibrated leak into the
LITERATURE CITED
(1) Kipping and Lloyd, J . Chem. Soc., 79,449 (1901). RECEIVED May 11, 1948. Presented before the Division of Bnnlytioal and Xlicro Chemistry a t the 113th Meeting of the AZlfERIcAN C H E M I C A L SOCIETY, Chicago, 111.
A Hood for Work with Radioactive Isotopes A . K. SOLOMON, Ehrvard Medical School, AND C . A. FOSTER, Harvard Unisersity, Boston, Mass. of the bottom is appreciably greater; in view of the oblique path the rays must take, the shielding is equivalent to approximately 12 inches of concrete plus the lead. The ceiling is also 8 inches thick, but has no lead because the floor of the storyabove is 5.5 feet above the top of the hood. The front of the hood is closed by 2.5 inehes of lead, cast in steel frames.
has been constructed for preliminary work with AHOOD radioactive material as required for small scale chemical and biological experiments. Because it was necessary to design the hood in advance of any exact knowledge of the intensity of the hourccs that mould bc handled, it was decided arbitrarily to debign it to accomniodate sources of intensity equal to 500 millicurics of radium. To date, there has been no occasion to handle illore than mc. of radioactive material, and the design has cordingly been simplified and modified for these less stringent requirements without affecting its possible later use for intense bOUrCeS. In vie,P of the widespread use of radioactive isotopes, and the published description of the hazards involved in their use ( I - S ) , it has seemed desirable to describe this installation. Figure 1, a dinwing of the hood as oiiginally designed, shows t h v setup for the niorr iiitcnw sources; Figure 2 shows thc hood a< inodified for Ion intolisity s o u r c ~ b .
Although the laboratory is on the ground floor, it was necessary to build concrete piers in the pipe space beneath it to support the 3.5-ton weight of the hood. Its position within the laboratory was chosen so that inverse square law protection would be available in addition to that provided by the concrete, as shown in Figure 3' Special precautions were taken with the services that enter and leave the hood* ii removable stainless steel pan with a I-inch turned-up lip rests on the bottom. Waste escapes through a stainless steel sink designed for removal and relatively easy replacement; it is backed by 0.5-inch lead sides and bottom. From the sink, the waste passes through a sediment trap before entering the soil line.
Thc sides, back, and bottom of the hood arc constructed of 8 inches of concrete and 0.5 inch of lead. The equivalent thickness 304
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