Cyanamide

Containing both a nucleophilic and electrophilic site within the same molecule, cyanamide undergoes various reactions with itself. Cyanamide exists as two tautomers, one with the connectivity N≡C–NH₂ and the other with the formula HN=C=NH ("carbodiimide" tautomer). The N≡C–NH₂ form dominates, but in a few reactions (e.g. silylation) the diimide form appears to be important.[3]

Cyanamide dimerizes to give 2-cyanoguanidine (dicyandiamide). This dimerization is hindered or reversed by acids and is inhibited by low temperatures. The cyclic trimer is called melamine.[3]

Cyanamide is produced by hydrolysis of calcium cyanamide, which in turn is prepared from calcium carbide via the Frank-Caro process.[4]

CaCN₂ + H₂O + CO₂ → CaCO₃ + H₂NCN

The conversion is conducted on slurries.

Cyanamide can be regarded as a functional single carbon fragment which can react as an electrophile or nucleophile. The main reaction exhibited by cyanamide involves additions of compounds containing an acidic proton. Water, hydrogen sulfide, and hydrogen selenide react with cyanamide to give urea, thiourea, and selenourea, respectively:

H₂NCN + H₂E → H₂NC(E)NH₂ (E = O, S, Se)

In this way, cyanamide behaves as a dehydration agent and thus can induce condensation reactions. Alcohols, thiols, and amines react analogously to give alkylisoureas, isothioureas, and guanidines. The anti-ulcer drug cimetidine is generated using such reactivity. Related reactions exploit the bifunctionality of cyanamide to give heterocycles, and this latter reactivity is the basis of several pharmaceutical syntheses such as the aminopyrimidine imatinib, and agrichemicals Amitrol and hexazinone. The hair-loss treatment minoxidil and the anthelmintics albendazole, flubendazole, and mebendazole feature 2-aminoimidazole substructures derived from cyanamide.[3] Cyanamide is also used in the synthesis of other pharmaceutical drugs including tirapazamine, etravirine, revaprazan, and dasantafil.

The cyanamide anion has the character of a pseudo chalcogen, cyanamide can therefore be regarded as analogue to water or hydrogen sulfide.

A convenient method for the preparation of secondary amines which are not contaminated with primary or tertiary amines is the reaction of cyanamide with alkyl halides to N,N-dialkylcyanamides which can easily be hydrolyzed to dialkylamines and then decarboxylated.[5] Cyanamide adds itself in the presence of N-bromosuccinimide to olefinic double bonds. The addition product is converted by bases to N-Cyanaziridine,[6] cyclized in the presence of acids to imidazolines, which can be further reacted to vicinal diamines by alkaline cleavage.[7]

Cyanamide is also a versatile synthetic building block for heterocycles: it forms 2-aminobenzimidazole with 1,2-diaminobenzene[8] and it forms with the readily available cyclic enamine 4-(1-cyclohexenyl)morpholine[9] and with elemental sulfur a 2-aminothiazole in good yields.[10]

Sodium dicyanamide is available in good yield and high purity from cyanamid and cyanogen chloride,[11][12] which is suitable as an intermediate for the synthesis of active pharmaceutical ingredients.[13] A guanidino group is introduced by reaction of cyanamide with sarcosine In the industrial synthesis of creatine:.[14]

This synthesis route mostly avoids problematic impurities like chloroacetic acid, iminodiacetic acid, or dihydrotriazine that occur in other routes. The physiological precursor guanidinoacetic is obtained analogously by reacting cyanamide with glycine.

Methods to stabilize cyanamide make it available on an industrial scale. Due to the strong affinity towards self-condensation in alkaline media (see above) solutions of cyanamide are stabilized by the addition of 0.5 wt% of monosodium phosphate as buffer. Solid cyanamide is produced by careful evaporation of the solvent and subsequent addition of a hydrolysis-labile ester of formic acid. The ester absorbs traces of moisture (suppression of urea formation), neutralizes alkalinity (ammonia) and continually releases small amounts of formic acid.[15]

Cyanamide degrades via hydrolysis to urea, an excellent fertilizer. Fungi, like Myrothecium verrucaria, accelerate this process utilizing the enzyme cyanamide hydratase.[18]

Cyanamide is the name for a functional group with the formula R¹R²N−C≡N where R¹ and R² can be a variety of groups. These compounds are called cyanamides. One example is naphthylcyanamide, C₁₀H₇N(CH₃)CN, which has been produced by the von Braun reaction,[19] a general method for the conversion of tertiary amines to cyanamides using cyanogen bromide as reagent.[20] Some cyanamides where R¹ and R² are identical alkyl groups are prepared directly by alkylation of a salt of the parent cyanamide.[11]

Due to its high permanent dipole moment (i.e., 4.32 ± 0.08 D),[21] cyanamide was detected in spectral emissions coming from the Sgr B2 molecular cloud (T < 100 K) through its microwave transitions as the first known interstellar molecule containing the NCN frame.[22]

It is used as an alcohol-deterrent drug in Canada, Europe, and Japan.[3]

Cyanamide has a modest toxicity in humans.[23] Workplace exposure to hydrogen cyanamide sprays or exposure in people living in the vicinity of spraying have been reported as causing respiratory irritation, contact dermatitis, headache, and gastrointestinal symptoms of nausea, vomiting, or diarrhea.[23]

• International Chemical Safety Card 0424
• NIOSH Pocket Guide to Chemical Hazards. "#0160". National Institute for Occupational Safety and Health (NIOSH).
• OSHA guideline for cyanamide