Alkyl cyanides isocyanides

The C chemical shifts of simple alkyl cyanides, isocyanides, isocyanates and isothiocyanates may be divided into two distinct groups. ... 

Haloalkanes react with KCN to form alkyl cyanides as main product Cxample 10.5 while AgCN forms isocyanides as the chief product. Explain. 

It would seem therefore that the only problem would be to determine whether they exist in the form of alkyl cyanides, i.e., with the hydrogen, potassium or silver linked to the carbon atom of the cyanogen or whether they are in the form of the alkyl isocyanides with the nitrogen atom of the cyanogen group linked to the other element. This, however, is where the facts become perplexing. 

Alkyl Cyanides from Potassium Cyanide.—That potassium cyanide has the constitution corresponding to an alkyl cyanide is supported by the fact that alkyl halides with potassium cyanide yield alkyl cyanides and not isocyanides. 

A free radical can add to CO or an isocyanide (RNC) in the course of a free-radical cyclization reaction, too, to give an acyl radical (RC=0) or an iminyl radical (RC=NR), either of which can undergo further reactions. In the following example, an alkyl radical adds to the terminal C of f-BuNC to give an iminyl radical. The iminyl radical then fragments to give t-Bu- and an alkyl cyanide N=CR. In a different substrate, the iminyl radical may undergo an addition or an abstraction reaction instead. 

Firstly, a group consisting of carbon monoxide, the cyanide ion and alkyl isocyanides, which exhibit chemical shifts in the range 12-37 p.p.m., and secondly a group made up of carbon dioxide, alkyl cyanides, isothiocyanates and the cyanate and thiocyanate ions with chemical shifts in the range 55-76 p.p.m. (from CS2). The groupings reflect similarities between the valence bond description of each set of compounds with their parent molecules, carbon monoxide and carbon dioxide. 

When an alkyl halide is treated with silver cyanide, reaction takes place in the usual way a silver halide and an organic compound are formed. The product, however, is not an alkyl cyanide, as is the case when potassium cyanide is used, but an isomeric compound. The substances prepared from silver cyanide are called isocyanides, isonitriles, or carbylamines. The last name is given to them on account of the fact that they unite with acids and thus resemble the amines. The addition-products do not, however, resemble salts in their chemical properties. When hydrogen chloride is passed into an ethereal solution of methyl isocyanide, a compound of the formula 2CH3NC.3HCI is formed, which is decomposed when brought into contact with water. 

On the basis of theoretical studies, it has been suggested that alkyl diazonium ions should undergo a rearrangement similar to the cyanide-isocyanide interconversion this reaction, which could only be detected by shift of labelled nitrogen, has not been observed. Reaction of a diazonium ion proceeds usually by one of four routes. 

Another method used to remove phosgene substitutes from the desired products is to destroy them with appropriate nucleophiles such as water or alcohols. This method can, of course, only be applied when the product is insensitive to these nucleophiles, as is the case for carbamates, carbonates, ureas, cyanides, isocyanides, and alkyl chlorides. Chloroformates, carbamoyl chlorides, isocyanates, acyl chlorides, N-carboxylic anhydrides, and carbodiimides, on the other hand, cannot be purified by this method. Consequently, a synthesis of these compounds using phosgene is worthy of consideration. 

ISONITRILES. This designation includes isocyanides (see Vol 3, C582-L to C583-L and Vol 7, I135-R for Cyanicic Acid and-Derivatives) and Carbylamines, R.NiC. The first isonitriles were prepd in 1886 by Gautier, by the action of Ag cyanide on alkyl iodides. Later, Hofmann prepd them by the action of chlf ale KOH on primary amines ... 

Silver(I) isocyanide complexes have been known for a long time and they were usually prepared by alkylation of silver cyanide.226 More recent reports include the study of steric effects of ligands... 

Imidazolines are also formed in silver cyanide-catalyzed cyclization of alkyl isocyanides with aliphatic diamines (Scheme 103).169 This simple synthesis can be applied in a general way with difunctional nucleophiles and has been used to prepare benzimidazoles, oxazoles, thiazoles, and oxazines.169 It is suggested that transient carbene complexes are formed in these reactions (cf. 87 in Scheme 103) but further work is required to ascertain the mechanism and scope of these processes. 

The scope of the silver cyanide-catalyzed reaction of difunctional nucleophiles with alkyl isocyanides has been described in the earlier section on imidazoles an example of the use of this simple approach in benzimidazole synthesis is illustrated in Scheme 105.169... 

It should be noted that the preparation of complexes (RNC)AuCN can be carried out via very special routes. Thus AuCN reacts with Mel to give (MeNC)AuCN. This reaction involves an interesting A-alkylation of an Au(i)-bound cyanide group.219 Other (RNG)AuGN complexes were obtained from the reaction of K[AuC14] with the isocyanide in methanol. Examples are the compounds (L)Au2(CN)2 with L = l,8-diisocyano-/>-menthane or 2,5-diisocyano-2,5-dimethyl-hexane. The reactions proceed with a dealkylation of an isocyanide in the coordination sphere of a gold(m) center to produce free cyanide (Scheme 53).201... 

Silver cyanide, reaction with alkyl halides in synthesis of isocyanides, 46, 77... 

Di-2-pyridyl sulphite (343) (from 2-pyridone and thionyl chloride in the presence of triethylamine) transforms primary aliphatic and aromatic amines RNH2 into N-sulphinylamines RN=S=0 and it dehydrates amides ArCONH2 to aryl cyanides, aldehyde oximes RCH=NOH (R = Cxlf 7. 4-MeOCgH4 or PhCH=CH) to the cyanides RCN and A-alkyl- and TV-ary Iformamides RNHCHO to isocyanides RNC. Aliphatic and aromatic... 

Silicon tetraisothiocyanate, reaction with 2,6-dimethylaniline to yield 2,6-diraethylphenyl thiourea, 46, 70 Silver cyanide, reaction with alkyl halides in synthesis of isocyanides, 46, 77... 

The well-known alkylation of ferrocyanide ion to form isocyanide iron complexes (48) can be explained by an insertion mechanism if the metal is alkylated initially, and then metal alkyl adds across a cyanide group. This mechanism also explains how external radioactive cyanide ion can enter the isocyanide ligands (48). 

Aromatic isocyanides can also be prepared conveniently by the dehydration of the corresponding formamides by phosphorus oxychloride, but much better results are obtained if the reaction is done in the presence of potassium fer/-butoxide rather than pyridine.6 Neither method of dehydrating formamides has yet been used to prepare methyl or ethyl isocyanide because their low boiling points make them difficult to isolate from the reaction mixture hence, until a suitable dehydration procedure is worked out, they are best made by reaction of the corresponding alkyl iodide with silver cyanide. ... 

Low oxidation states are generally stabilized by ligands which have both a donor (lone pairs) and n acceptor (either empty d orbitals or empty antibonding Jt orbitals) capability. Examples of common ligands with these characteristics are carbon monoxide, cyanide ion, alkyl and aryl isocyanides, tertiary phosphines and arsines, and alkyl or aryl phosphites. 

C N cyanide, thiocyanide complex N=C alkyl isocyanide 2200-2000 2183-2150 2166 Methyl isocyanide... 

Methyl isocyanide has been prepared chiefly by minor modifications of the original method of Gautier,3 which is the alkylation of silver cyanide by an alkyl halide. 

Though alkylation of metal cyanides is one of the oldest routes to metal-isocyanide complexes, at the present time the usefulness of this method is confined to (i) partially characterizing new metal-cyanide complexes, (ii) providing access to complexes containing unstable or unusual isocyanide ligands which cannot be prepared by direct interactions of complex with isocyanide, and (iii) providing a route to chiral metal-isocyanide complexes. The following examples exemplify this. 

Alkylation of the cyanide ligands in Ag4M(CN)8 with RX (X = halides) has provided the only route to the complexes M(CN)4(CNR)4 (M = Mo, W R = alkyl, allyl, CH2Ph, CPh3) (72, 73), as direct reaction of isocyanides on the cyanide anions has given only reduced products (74). 

Other examples of isocyanide complexes formed from cyanide alkylations are [CpFe(CO)(CNEtXPPh3)]+ (83), fram-[Pt(CNMe)2(PMe2Ph)2]-(SF03)2 (84), and PtI2(CNMe)2 (85). 

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