chemical physics of discharges - Argonne National Laboratory
chemical physics of discharges - Argonne National Laboratory chemical physics of discharges - Argonne National Laboratory
126 Conversion of Mixtures into More Complicated Molecules mien mixtures of relatively simple hydrides are passeq through an electric discharge, higher molecular weight ternary hydrides are formed. Thus by using appropriate mixtures of SiH4, GeH4, PH3, and AsH3, it has been possible to prepare, among other things, SiH3GeH3, SiH3PH2, SiHdsH2, GeHsPH2, and GeHdsH2. By using a silent electric discharge, which does not cause drastic fragmentation and rearrange- ment, it is possible, within limits, to tailor-make molecules. Thus a mixture of SiH3PH2 and SiH4 yields (SiH3)2PH, and a mixture of Si2E6 and Ph3 yields SizH5PH2. Passage of diborane-acetylene mixtures through an electric discharge yields carboranes as the major volatile products, including : 1, 5-C2B3H5, 1,6-C2B4H6, 2, ~ - C E B ~ and H ~ at ~ least six B-methylated derivatives of these plus C,3-(CH3)2-1,2-C2B3H3. The reaction of SiH, and (CH3)zO in a silent electric discharge yields mainly a series of inseparable mixtures, but a fair yield of SizHsCH3 can be isolated. A fascinating series of oxygen fluorides (02F2, 032, 04F2, O5F2 and 06F.7) has been prepared by subjecting mixtures of oxygen and fluorine to electric discharge at very low temperatures. All these compounds are very unstable, and, on warming, they decompose to oxygen and fluorine. Nitrogen trifluoride, AsF5, and F2 when subjected to a glow discharge at low temperatures yields NF4AsF6. This material is a relatively stable material which is fairly well characterized. The only reported method for the preparation of a xenon compound that does not involve the use of elementary fluorine or some fluorinating agent almost as difficult to handle as fluorine, is the electric discharge synthesis of XeF2 from Xe and CF4. The carbon-containing by-products of the reaction were not identified. Controlled Reactions of Atoms and Radicals with Other Species ' In the discharge methods discussed above, all the reactant species are passed through an electric discharge. However many synthetically useful reactions can be carried out in the absence of a discharge by allowing a stream of atoms or radicals (prepared in an electric discharge) to impinge on various compounds. For example, atomic hydrogen is a very reactive species which has been used for the preparation of hydrides and for carrying out reductions. promising field of study is the reaction of atomic hydrogen with aqueous solutions. In basic solutions, the hydrogen atoms yield electrons, and the method furnishes a convenient method for studying the reducing effects of the aqueous electron. A I
i \ ’. I i t 127 Atoms arid radicals act as electrophilic reagents. The atoms 0, C1, Br, I, and N favor attack at polarizable donor atorps. Thus atomic nitrogen reacts with divalent sulfur compounds (HzS, Cs2, OCS, Sa, S2Cl2 and SC12) to yield sulfur-nitrogen compounds, whereas no sulfur-nitrogen compounds are formed in the reaction of N atoms with SOe, SOC12, and SO>. The reaction with s2C12 gives fair yields of the interesting molecule NSC1. Equipment Most of the readily-available laboratory equipment for producing electric discharges is suitable only for relatively small-scale operation, involving only a gram or two of material. Such equipment, and the corresponding low yields, is satisfactory for the preparation of new compounds in amounts satisfactory for identification purposes. But in order for electric discharge syntheses to be useful for the preparation of mole quantities of materials, as are the usual synthetic methods, it will be necessary to have a marked break-through in the development and marketing of these instruments.
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126<br />
Conversion <strong>of</strong> Mixtures into<br />
More Complicated Molecules<br />
mien mixtures <strong>of</strong> relatively simple hydrides are passeq through<br />
an electric discharge, higher molecular weight ternary hydrides are<br />
formed. Thus by using appropriate mixtures <strong>of</strong> SiH4, GeH4, PH3, and<br />
AsH3, it has been possible to prepare, among other things, SiH3GeH3,<br />
SiH3PH2, SiHdsH2, GeHsPH2, and GeHdsH2. By using a silent electric<br />
discharge, which does not cause drastic fragmentation and rearrange-<br />
ment, it is possible, within limits, to tailor-make molecules. Thus<br />
a mixture <strong>of</strong> SiH3PH2 and SiH4 yields (SiH3)2PH, and a mixture <strong>of</strong><br />
Si2E6 and Ph3 yields SizH5PH2.<br />
Passage <strong>of</strong> diborane-acetylene mixtures through an electric<br />
discharge yields carboranes as the major volatile products, including :<br />
1, 5-C2B3H5, 1,6-C2B4H6, 2, ~ - C E B ~ and H ~ at ~ least six B-methylated<br />
derivatives <strong>of</strong> these plus C,3-(CH3)2-1,2-C2B3H3. The reaction <strong>of</strong><br />
SiH, and (CH3)zO in a silent electric discharge yields mainly a<br />
series <strong>of</strong> inseparable mixtures, but a fair yield <strong>of</strong> SizHsCH3 can be<br />
isolated.<br />
A fascinating series <strong>of</strong> oxygen fluorides (02F2, 032, 04F2,<br />
O5F2 and 06F.7) has been prepared by subjecting mixtures <strong>of</strong> oxygen<br />
and fluorine to electric discharge at very low temperatures. All<br />
these compounds are very unstable, and, on warming, they decompose<br />
to oxygen and fluorine. Nitrogen trifluoride, AsF5, and F2 when<br />
subjected to a glow discharge at low temperatures yields NF4AsF6.<br />
This material is a relatively stable material which is fairly well<br />
characterized.<br />
The only reported method for the preparation <strong>of</strong> a xenon compound<br />
that does not involve the use <strong>of</strong> elementary fluorine or some<br />
fluorinating agent almost as difficult to handle as fluorine, is<br />
the electric discharge synthesis <strong>of</strong> XeF2 from Xe and CF4. The<br />
carbon-containing by-products <strong>of</strong> the reaction were not identified.<br />
Controlled Reactions <strong>of</strong> Atoms and Radicals<br />
with Other Species '<br />
In the discharge methods discussed above, all the reactant<br />
species are passed through an electric discharge. However many<br />
synthetically useful reactions can be carried out in the absence <strong>of</strong><br />
a discharge by allowing a stream <strong>of</strong> atoms or radicals (prepared in<br />
an electric discharge) to impinge on various compounds. For example,<br />
atomic hydrogen is a very reactive species which has been used for<br />
the preparation <strong>of</strong> hydrides and for carrying out reductions.<br />
promising field <strong>of</strong> study is the reaction <strong>of</strong> atomic hydrogen with<br />
aqueous solutions. In basic solutions, the hydrogen atoms yield<br />
electrons, and the method furnishes a convenient method for studying<br />
the reducing effects <strong>of</strong> the aqueous electron.<br />
A<br />
I