Reduction of isocyanates

Reaction between alkyl halides and cyanide ion Elimination of water from N-alkylformamides Reduction of isocyanates... 

Reduction of isocyanates 6-36 Addition of Grignard reagents to isocyanates... 

Oxidative cleavage of amines 9-39 Reduction of amides 9-47 Reduction of nitro compounds 9-50 Reduction of nitroso compounds or hydroxylamincs 9-51 Reduction of oximes 9-52 Reduction of azides 9-53 Reduction of isocyanates, isothiocyanates, or N-nitroso compounds 9-55 Reduction of amine oxides 9-59 Reduction of azo, azoxy, or hydrazo compounds... 

Isocyanides, Isocyanates, RN=C=0, and alkyl carbamates, R NHCOOR2, are reduced to isocyanides, RN=C, by treatment with trichlorosilane and triethylam-ine in OH, Cl, in yields of 4(l 70%. r-Butyldiphenylsilyllithium2 also effects reduction of isocyanates to isocyanides, but this reagent is less convenient to use. 

There are few methods known for the reduction of isocyanates to isocyanides two novel methods now increase the scope of this transformation. Thus, both diphenyl-t-butylsilyl-lithium and trichlorosilane-triethylamine reduce isocyanates to isocyanides in high yield under mild conditions. 

Other common syntheses include the reduction of isocyanates [10] and nucleophilic displacement of alcohols [11]. Yet the most common method to synthesize isocyanides is via the dehydration of formamides (Scheme 7.2). This route (Method A), though more efficient than the previous syntheses, is undesirable due to the use... 

Industrially, polyurethane flexible foam manufacturers combine a version of the carbamate-forming reaction and the amine—isocyanate reaction to provide both density reduction and elastic modulus increases. The overall scheme involves the reaction of one mole of water with one mole of isocyanate to produce a carbamic acid intermediate. The carbamic acid intermediate spontaneously loses carbon dioxide to yield a primary amine which reacts with a second mole of isocyanate to yield a substituted urea. 

Naphthalenesulfonic acid can be converted to l-naphthalenethiol/T25 -J6 - by reduction of the related sulfonyl chloride this product has some utihty as a dye intermediate, and is converted by reaction with alkyl isocyanates to 3 -naphthyl-A/-alkylthiocarbamates, which have pesticidal and herbicidal... 

AletalHydrides. Metal hydrides can sometimes be used to prepare amines by reduction of various functional groups, but they are seldom the preferred method. Most metal hydrides do not reduce nitro compounds at all (64), although aUphatic nitro compounds can be reduced to amines with lithium aluminum hydride. When aromatic amines are reduced with this reagent, a2o compounds are produced. Nitriles, on the other hand, can be reduced to amines with lithium aluminum hydride or sodium borohydride under certain conditions. Other functional groups which can be reduced to amines using metal hydrides include amides, oximes, isocyanates, isothiocyanates, and a2ides (64). 

Iodine azide, on the other hand, forms pure adducts with A -, A - and A -steroids by a mechanism analogous to that proposed for iodine isocyanate additions. Reduction of such adducts can lead to aziridines. However, most reducing agents effect elimination of the elements of iodine azide from the /mwj -diaxial adducts of the A - and A -olefins rather than reduction of the azide function to the iodo amine. Thus, this sequence appears to be of little value for the synthesis of A-, B- or C-ring aziridines. It is worthy to note that based on experience with nonsteroidal systems the application of electrophilic reducing agents such as diborane or lithium aluminum hydride-aluminum chloride may yet prove effective for the desired reduction. Lithium aluminum hydride accomplishes aziridine formation from the A -adducts, Le., 16 -azido-17a-iodoandrostanes (97) in a one-step reaction. The scope of this addition has been considerably enhanced by the recent... 

Isocyanates and isothiocyanates are reduced to methylamines on treatment with LiAlH4. Lithium aluminium hydride does not usually reduce azo compounds (indeed these are the products from LiAlH4 reduction of nitro compounds, 19-59), but these can be reduced to hydrazo compounds by catalytic hydrogenation or with... 

An in situ infrared investigation has been conducted of the reduction of NO by CH4 over Co-ZSM-5. In the presence of O2, NO2 is formed via the oxidation of NO. Adsorbed NO2 then reacts with CH4. Nitrile species are observed and found to react very rapidly with NO2, and at a somewhat slower rate with NO and O2. The dynamics of the disappearance of CN species suggests that they are reactive intermediates, and that N2 and CO2 are produced by the reaction of CN species with NO2. While isocyanate species are also observed, these species are associated with A1 atoms in the zeolite lattice and do not act as reaction intermediates. A mechanism for NO reduction is proposed that explains why O2 facilitates the reduction of NO by CH4, and why NO facilitates the oxidation of CH4 by O2. 

Figure 3.7. In-situ reflection-absorption infrared (RAIRS) spectra as a function of catalyst temperature from a Pd(lll) single-crystal surface in the presence of a NO + CO gas mixture (240mbar, Pco/Pno = 1-5) [66]. The data clearly show the appearance of an isocyanate-related band at 2256 cm-1 at temperatures above 500 K. In-situ spectroscopic experiments such as these have proven indispensable to detect and identify key reaction intermediates for the catalytic reduction of NO on metal surfaces. (Figure provided by Professor Goodman and reproduced with permission from the American Chemical Society, Copyright 2003).

A few additional points have also been raised by specific surface-science work concerning the catalytic reduction of NO. For instance, it has been widely recognized that the reaction is sensitive to the structure of the catalytic surface. It was determined that rough surfaces such as (110), or even (100), planes enhance NO dissociation over flatter (111) surfaces, and also favor N2 desorption instead of N20 production. On the other hand, NO dissociation leads to poisoning by the resulting atomic species, hence the faster reaction rates seen with medium-size vs. larger particles on model rhodium supported catalyst (the opposite appears to be true on palladium). Also, at least in the case of palladium, the formation of an isocyanate (-NCO) intermediate was identified... 

Reductive carbonylation of nitro compounds (in particular aromatic dinitro compounds) is an important target in industry for making diisocyanates, one of the starting materials for polycarbamates. At present diisocyanates are made from diamines and phosgene. Direct synthesis of isocyanates from nitro compounds would avoid the reduction of nitro compounds to anilines, the... 

The synthesis of 3-H-oxazol-2-ones was described by Nam et al. [69]. The substituted benzoin 89 was formed from the coupling of 3,4,5-trimethoxy-benzaldehyde 18 with 3-nitro-4-methoxybenzaldehyde, Scheme 22. Reaction with PMB-isocyanate and subsequent cyclization gave the protected oxazolone derivative 90. The PMB group was removed by reflux in TFA and reduction of the nitro-group was performed using Zn to give the combretoxazolone-aniline 91. 

N-Methylethylamine has been prepared by heating ethyl-amine with methyl iodide in alcohol at 100° 3 by the hydrolysis of N-methyl-N-ethylarenesulfonamides,4-5 -nitroso-N-methyl-N-ethylaniline,6 or methylethylbenzhydrylidene ammonium iodide 7 by catalytic hydrogenation of ethyl isocyanate or ethyl isocyanide 8 and by the reduction of ethyl isocyanate by lithium aluminum hydride,9 of N-methylacetisoaldoxime by sodium amalgam and acetic acid,10 or of a nitromethane/ethylmagnesium bromide adduct by zinc and hydrochloric acid.11... 

The method gives better yields, utilizes more readily available starting materials, and is much less laborious than the hydrolysis of N-methyl-N-alkylarenesulfonamides and -nitroso-N, N-di-alkylanilines, or the lithium aluminum hydride reduction of alkyl isocyanates. Compared to the closely related procedure of Lucier, Harris, and Korosec,12 in which the N-benzylidenealkyl-amine is treated with dialkyl sulfate at atmospheric pressure, the present procedure tends to give higher yields and purer products, but it is less convenient because of the need for a pressure vessel. 

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