Phosphorus arsenic hydrides

Explosion Hazard The volatile hydrides (such as hydrides of boron, arsenic, phosphorus, selenium, tellurium) form explosive mixtures with air. 

Compare the properties of antimony hydride with those of similar compounds of arsenic, phosphorus, and nitrogen (the thermal stability, reducing properties, etc.). 

Antimony Hydride, SbHj.—It corresponds to phosphorus hydride (PHj) and arsenic hydride (AsHj). It was discovered by Lewis Thompson in 1837, and about the same time independently by PfafF. However, the production of pure antimony hydride and the determination of its physical constants are matters of recent times. 

Alkyl-combination.—Antimony hydride (SbHj), like arsenic hydride (AsHg) and phosphorus hydride (PHj), can give rise to organic compounds in which the H-component is replaced by an alkyl. It is then called stihirte. It can be produced by allowing iodine-alkyls to act upon potassium antimonide or upon sodium antimom de, or by the reaction between antimony chloride and zinc-alkyls. 

All major ash elements and some trace elements are determined in coal or fly ash by inductively coupled plasma emission spectrometry. Parr oxygen bomb combustion followed by ion selective electrode. X-ray fluorescence or atomic absorption spectrom-etric measurements are used to determine halogens, sulfur, nitrogen, mercury, arsenic, selenium, and phosphorus. Hydride generation-atomic absorption spectrometry is used to determine traces of As,... 

Nitrogen, phosphorus and arsenic form more than one hydride. Nitrogen forms several but of these only ammonia, NHj, hydrazine, N2H4 and hydrogen azide N3H (and the ammonia derivative hydroxylamine) will be considered. Phosphorus and arsenic form the hydrides diphosphane P2H4 and diarsane AS2H4 respectively, but both of these hydrides are very unstable. 

Optional experiment. When all the air has been displaced, collect a test-tube of the gas over water (by appropriate inclination of the end of the delivery tube beneath the mouth of a test-tube filled with water and supported in a beaker of water). Observe the colour and odour of the gas. Ignite the test-tube of gas, and note the luminosity of the flame and the amount of carbon deposited. Pure acetylene is almost odourless the characteristic odour observed is due to traces of hydrides of phosphorus, arsenic and sulphur. 

To be useful as CVD precursors, a metallo-organic compound should be stable at room temperature so that its storage and transfer are not a problem. It should also decompose readily at low temperature, i.e., below 500°C. The compounds listed in Table 4.1 meet these conditions with the exception of the alkyls of arsenic and phosphorus, which decompose at higher temperatures. For that reason, the hydrides of arsenic and phosphorus are often preferred as CVD precursors (see Ch. 3). These hydrides however are extremely toxic and environmental considerations may restrict their use. 

C. Helling, V. Imhof, L. Nielsen, and E. Jacobson Complex Alumino-Hydrides containing Nitrogen, Phosphorus and Arsenic. Inorg. Chem. 2, 504 (1963). 

Reactions similar to these provide convenient syntheses of hydrides of such elements as phosphorus, arsenic, tellurium, and selenium, because these elements do not react directly with hydrogen and the hydrides are unstable. 

Intimate mixtures of chlorates, bromates or iodates of barium, cadmium, calcium, magnesium, potassium, sodium or zinc, with finely divided aluminium, arsenic, copper carbon, phosphorus, sulfur hydrides of alkali- and alkaline earth-metals sulfides of antimony, arsenic, copper or tin metal cyanides, thiocyanates or impure manganese dioxide may react violently or explosively, either spontaneously (especially in presence of moisture) or on initiation by heat, friction, impact, sparks or addition of sulfuric acid [1], Mixtures of sodium or potassium chlorate with sulfur or phosphorus are rated as being exceptionally dangerous on frictional initiation. 

Toxicity Variable. The hydrides of phosphorus, arsenic, sulfur, selenium, tellurium and boron which are highly toxic, produce local irritation and destroy red blood cells. They are particularly dangerous because of their volatility and ease of entry into the body. The hydrides of the alkali metals, alkaline earths, aluminum, zirconium and titanium react with moisture to evolve hydrogen and leave behind the hydroxide of the metallic element. This hydroxide is usually caustic. See also sodium hydroxide... 

Table 6.4 contains some bond length and bond angle data for the hydrides, fluorides and chlorides of nitrogen, phosphorus and arsenic. The differences in the electronegativity coefficients (Allred-Rochow) in the compounds are also given. 

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