Cyanide criteria

Federal drinking water standards for cyanide have been withdrawn and are not included in the latest publication. The Public Health Service limit for drinking water had been 200 ppb. Whether the limit was expressed as free or total cyanide was in question at the time. The fresh water aquatic cyanide criterion is 3.5 ppb as a 24-hour average, not to exceed 52 ppb at any time. 

The potential substrates for the Strecker reaction fall into two categories ald-imines (derived from aldehydes, for which cyanide addition results in formation of a tertiary stereocenter) and ketoimines (derived from ketones, for which addition results in a quaternary stereocenter). As in the case of carbonyl cyanation, significant differences are observed between the substrate subclasses. To date, while a few catalyst systems have been found to display broad substrate scope with respect to aldimine substrates, successful Strecker reactions of ketoimines have been reported in only two cases. As is the case for all asymmetric catalytic methodologies, the breadth of the substrate scope constitutes a crucial criterion for the application of the Strecker reaction to a previously unexplored substrate. 

Carbon forms a nitride, cyanogen, which is related to hydrogen cyanide. Both cyanogen and hydrogen cyanide are potential fuels, but both are extremely toxic and can be rejected based on the third criterion. Carbon disulfide is a room temperature liquid with fuel properties. It is less toxic than cyanogen, but is sufficiently toxic to be rejected because of the third criterion. When it bums, it produces large amounts of toxic sulfur dioxide. Nitrogen sulfide is an explosive solid. 

A general classification scheme for the discussion of the properties of mixed valence compounds has been introduced by Robin and Day 17). Although by no means all the deeply colored transition metal cyanides M [BM(CN) ]2H2O are mixed valence compounds in the strict sense, we will use this classification scheme for the whole group. The classification of the polynuclear cyanides is made on a purely phenomenological basis using the electronic spectra as a criterion. 

From the viewpoint of chemical and physical requirements the permissible indicators involve a number of criteria mercury, selenium, cadmium, vanadium, chromium, arsenic, silver, lead, barium, cyanides, hydrogen sulphide, fluorides, phenols, oil and oil substances, COD(Mn), colour, odour, taste and turbidity. The most stringent criterion concerns the content of mercury, followed by selenium, cadmium, vanadium, cyanides, oil and oil substances. Another important indicator is the content of organic matters characterized by COD(Mn). 

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