Lead cyanamide

Lead cyanamide [20837-86-9], PbCN2, Mr 247.23, is a lemon yellow powder. Zinc cyanamide [20654-08-4], ZnCN2, Mr 105.41, is a white to beige powder. Their properties are listed in Table 47 [5.125],... 

Cyanamide pigments are produced from industrial-grade calcium cyanamide which is first dissolved. Sulfide and phosphide impurities are precipitated as iron or lead salts [5.127]—[5.132] or oxidized [5.133] [5.135] and filtered off together with graphite impurities. The pure calcium cyanamide is reacted in an aqueous medium with soluble lead or zinc salts or with a slurry of lead oxide or zinc oxide [5.127], [5.129], [5.133], [5.136]—[5.138]. The pigments are filtered, washed, dried, and ground. Zinc cyanamide [5.139] and pure lead cyanamide are not explosive. An explosion reported during the production of lead cyanamide was caused by contamination with small amounts of acid or nitrates [5.140],... 

Zinc cyanamide is nontoxic, but the toxicological classification of lead cyanamide has to take its lead content into account. For toxicological data, see Section 5.2.14. 

For very specific and limited applications the following lead-based products have been used lead suboxide, lead carbonate and lead cyanamide (mirror coatings), lead silicate (electro disposition primers), dibasic lead phosphate, tribasic lead phosphate silicate, and calcium plumbate [5.51, 5.53]. 

Zinc cyanamide (Zn(CN)2) was developed as a replacement for lead cyanamide (see Section 5.2.4.1) mainly for application in mirror coatings. The electrochemical effectiveness of cyanamides is attributed to a passivation action under alkaline conditions [5.56]. 

Zinc cyanamide is produced on an industrial scale from pure calcium cyanamide in an aqueous medium with zinc salts or a slurry of zinc oxide [5.56]. The pigment has, until now, not reached the importance of lead cyanamide for application in mirror coatings. 

A column (about 25 mm od X 300 mm long), packed loosely with glass wool and lead cyanamide (about 25 g, Alfa Inorganics Inc., Beverly, MA ), is attached to a vacuum line and evacuated for about 2 hours. lodogermane (GeH3l 0.10l... 

Lead chromate (VI) oxide Lead chromate, red. See Lead chromate oxide Lead cyanamide CAS 35112-70-0... 

The Colour Index (1971) lists this compound under Cl 77610/Pigment Yellow 48, describing it as lead cyanamide , with a formula Pb(CN)2. Preparation is by extracting commercial calcium cyanamide with water, adding a little lead nitrate to precipitate the black sulfides, then filtering and heating the filtrate with lead nitrate and ammonia to precipitate the yellow lead cyanide. Use and other terminology is currently unknown. 

Handling and Storage. Cyanamide solution dimerizes to dicyandiamide and urea with the evolution of heat and a gradual increase in alkalinity accelerating the reaction. Storage above 30°C without pH stabilizer leads to excessive dimerization and can result in violent exothermic polymerization. Cyanamide should be stored under refrigeration and the pH tested periodically. Stabilized cyanamide can be kept at ambient temperature for a few weeks. 

Sodium borohydride reduction of 4-substituted isoquinolinium salts led to vinylogous cyanamides, ureas, and urethanes, as well as the corresponding tetrahydroquinolines (640). Hydrogenation of /8-acylpyridinium salts (641) to vinylogous ureas was exploited in syntheses of alkaloids (642), leading, for instance, to lupinine, epilupinine, and corynantheidine (643, 644). Similarly, syntheses of dasycarpidone and epidasycarpidone were achieved (645) through isomerization of an a,/0-unsaturated 2-acylindole and cyclization of the resultant enamine. 

The acylation of enamines derived from cyclic ketones, which can lead to the acyl ketone or ring expansion (692-694), was studied by NMR and mass spectroscopic analysis of the products (695,696). In a comparative study of the rates of diphenylketene addition to olefins, a pronounced activation was observed in enamines (697). Enamine N- and C-acylation products were obtained from reactions of Schiff s bases (698), vinylogous urethanes (699), cyanamides (699), amides (670,700), and 2-benzylidene-3-methylbenzothiazoline (672) with acid chlorides, anhydrides, and dithio-esters (699). 

The new phosphazene triazene hybrid ring compound (42) can be obtained from cyanamide by two slightly different routes, A96 and B97 (Scheme 11). Substitution of ammonia in route B leads to further ring compounds (43) and (44a, b).97... 

The strongly acidic character of cyanamide, compared with simple amines, results in its facile dialkylation by a range of reagents [24], Reaction with a,(o-dihalogeno compounds leads to cyclic products (Table 5.4). 

Guanidines have been prepared by the reaction between an amine, or an amine salt, and a host of other reagents, such as a thiourea in the presence of lead or mercuric oxide [83, 157, 158], carbodi-imides [140, 174, 175],calcium cyanamide [176, 177], isonitrile dichlorides [178—180], chloroformamidines [181], dialkyl imidocarbonates [182], orthocarbonate esters [183], trichloro-methanesulphenyl chloride [184], and nitro- or nitroso-guanidines [185-188]. Substituted ureas can furnish guanidines, either by treatment with amines and phosphorus oxychloride [189], or by reaction with phenylisocyanate [190] or phosgene [191]. 

However, hydrolysis of the oxime of 3-benzoyl-5-phenyl oxadiazole leads to benzoyl cyanamide (76). 

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