Drying agents/dessicants

Table 19.21. Performances and selected properties of drying agents and dessicants... 

All materials used in isotopic analysis should be dried scrupulously by sublimation in vacuo or distillation from drying agents. For accurate work the tubes should be heated to S00°C. in vacuo before use and stored in a dessicator. It should be remembered that if gaseous or very volatile products are formed on heating, the sealed tubes are sometimes liable to explode and appropriate precautions should be taken. 

An accident of the same nature happened when it was dried with diphosphorus pentoxide. In this case, it is unlikely that the reason for it is the formation of an acetylene salt. The author believes that, since water plays a desensitising role on this compound, it leads to a very unstable pure alcohol when it is removed by strong dehydrating agents. The temperature rise due to the dessicating agent hydration is sufficient to decompose the pure alcohol violently.This interpretation could also be applied to the previous case. 

In anionic solution systems the feed stocks are typically dried over various types of dessicants because the systems are sensitive to water contamination. When using continuous anionic solution polymerization systems, it is necessary to employ low (ppm) concentrations of a chain-transfer agent in order to discourage gelation and fouling 1,2-butadiene is often used for this purpose in commercial applications. Alkyl-lithium-initiated polybutadiene is less prone to contain gel and does not contain the heavy metal catalyst residues associated with Ziegler-Natta catalyzed products. 

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