Amines, primary dehydrogenation

Interestingly, persulfate reacts differently with aliphatic and aromatic amines. Aliphatic primary amines are dehydrogenated to imines and further converted to aldehydes when reacted with peroxy disulfate , whereas aromatic primary amines are oxidized to nitroso compounds using potassium persulfate in the presence of H2SO4 (equation 14) °. 

Primary amines are dehydrogenated by high-valent oxometal species to give nitriles, or imines depending on the number of available a-hydrogens. Oxidation of the amine via peroxometal-intermediates (e.g. with MTO, Na2Mo04,... 

Amines. Primary amines, RNHj, where R is alkyl, arylalkyl, or cycloalkyl, when boiled with Raney nickel (no Hj) are converted into the secondary amine (80% yield) and some tertiary amine (10%). n-Hexylamine —> di-n-hexylamine (70%) and tri-n-hexylamine (9%). The reaction is considered to involve dehydrogenation to the aldimine followed by addition of the starting amine, elimination of ammonia, and hydrogenation. 

Dienophile. This polycarbonyl compound forms Diels-Alder adducts, which are versatile intermediates for various syntheses. For example, an indoxyl derivative is accessible on reaction of its butadiene adduct with a primary amine and dehydrogenation. 

Complexes of ruthenium and rhodium have been identified that catalyze the hydrogenation of nitriles under mild conditions with very good selectivities to the primary amine. In particular, Otsuka and co-workers showed that [RhHfP Prj) ] catalyzes the hydrogenation of a variety of nitriles to amines under mild conditions (1 atm pressure, 20 °C, 2 h Equation 15.119). The reaction is reversible primary amines undergo dehydrogenation in the presence of [Rl iHfP Prj) ] to form nitriles (Equation 15.120). Iridium catalysts for the dehydrogenation of nitriles have also been reported recently. ... 

Jun CH, Chung KY, Hong JB (2001) C-H and C-C bond activation of primary amines through dehydrogenation and transimination. Org Lett 3 785... 

A similar dehydrogenation of an amine (primary or secondary amine) to imine with catalyst 1 was used by Beller to alkylate indoles (9) [50]. The imine reacts with the indole to give an aminoalkylated intermediate, which undergoes elimination of ammonia or amine to give an oxidized indole intermediate. The hydrogens removed from the amine are now added back to the latter intermediate to give the indole product so in this case the overall reaction is not an oxidation. 

When additional substituents ate bonded to other ahcycHc carbons, geometric isomers result. Table 2 fists primary (1°), secondary (2°), and tertiary (3°) amine derivatives of cyclohexane and includes CAS Registry Numbers for cis and trans isomers of the 2-, 3-, and 4-methylcyclohexylamines in addition to identification of the isomer mixtures usually sold commercially. For the 1,2- and 1,3-isomers, the racemic mixture of optical isomers is specified ultimate identification by CAS Registry Number is fisted for the (+) and (—) enantiomers of /n t-2-methylcyclohexylamine. The 1,4-isomer has a plane of symmetry and hence no chiral centers and no stereoisomers. The methylcyclohexylamine geometric isomers have different physical properties and are interconvertible by dehydrogenation—hydrogenation through the imine. 

A reaction that involves dehydrogenation to an imine, which then reacts further is the reaction of primary or secondary amines with palladium black. The imine initially formed by the dehydrogenation reacts with another molecule of the same or a different amine to give an aminal, which loses NH3 or RNH2 to give a secondary or tertiary amine. An example is the reaction between V-methylbenzylamine and... 

Petrillo reports that the reaction of l,4-diaryl-2,3-dinitrobutadienes 42 with representative primary amines leads to //-alkyl-3-alkylamino-2,5-diaryl-4-nitropyrrolidines 43 presumably via a disfavored 5-endo-trig ring closure <00EJOC903>. Acid catalyzed elimination of the amine led to the corresponding trans-2,5-diaryl-3-nitro-3-pyrrolines 44 which could be dehydrogenated to the corresponding pyrroles 45. 

The meso-ionic l,3>2-oxathiazol-5-ones (169) show an interesting range of reactions with nucleophiles including ammonia, primary amines, and aqueous alkali. They also react with l,3-dipolarophiles, including dimethyl acetylenedicarboxylate and methyl propiolate, yielding isothiazoles (171) and carbon dioxide. 1,3-Dipolar cycloaddition reactions with alkenes such as styrene, dimethyl maleate, and methyl cinnamate also lead to isothiazoles (171) directly. BicycUc intermediates (cf. 136) were not isolable these cycloaddition reactions with alkenes giving isothiazoles involve an additional dehydrogenation step. 

Synthesis of secondary amides via the oxidative coupling (dehydrogenation) of primary alcohols R CH3(OH) and primary amines R (CH3)NH3 to the amides... 

A useful example is the oxidative dehydrogenation of primary amines to nitriles. The amine (2 mmol) is added dropwise or in small portions to a vigoronsly stirred solutuion of [RnO ] prepared as above (100 cm ) the reaction is complete when the dark orange colonr of [RuO ] reappears. The solution is extracted with dieth-ylether (3x25 cm ), dried over MgSO and the ether removed [549]. 

Primary amines can be dehydrogenated under mild conditions and in high yields to nitriles at the nickel hydroxide electrode (Eq. (9)). Short chain and reactive amines are already oxidized at 5 °C, whilst long chain amines need somewhat higher temperatures. Diamines are converted smoothly to dinitriles (Table 13). 

Primary amines at a primary carbon can be dehydrogenated to nitriles. The reaction has been carried out with a variety of reagents, among others, IF5,"9 lead tetraacetate, 20 nickel peroxide,121 NaOCl in micelles,122 S g-NiSO, 2-1 and CuCl-02-pyridine.124 Several methods have been reported for the dehydrogenation of secondary amines to imines.125 Among them126 are treatment with(l) iodosylbenzene PhIO alone or in the presence of a ruthenium complex, 27 (2) Me2SO and oxalyl chloride, 2" and (3) f-BuOOH and a rhenium catalyst. 29... 

TV-Alkylidenalkylamines were found in the reaction products of the transformation of 1-butylamine [147,148], cyclohexylamine and isopropylamine [149] on alumina, and were probably formed by the dehydrogenation of the primary amine to an imine, followed by its condensation with a second molecule of the amine [148], rather than by the dehydrogenation of the dialkylamine [147], The TV-alkylidenalkylamines R=N—R decompose to an olefin and an imine a cyclic process has been postulated [148] which explains the increases in reactivity of amines with secondary alkyls. Also butyronitrile has been detected in appreciable amounts in the reaction products of 1-butylamine on alumina at 500° C [147],... 

Table 1 shows that methyl dodecanoate is easily converted into amine in the presence of CuCr deposited on alumina or on titania. Nevertheless one can observe that the methylation reaction is rather difficult and favoured by alumina. Moreover, a significant increase of N-dimethyl dodecylamine is obtained when the reaction is carried out with a large excess of hydrogen. Due to the mechanism of the reaction this is unexpected indeed it is generally considered that the methylation of primary amine with methanol requires i) the dehydrogenation of alcohol into a carbonyl compound and ii) a further reaction of this compound with primary amine or secondary amine via imine or enamine intermediates. 

In this case the final dehydrogenation of 1,2-dihydroquinaldine to quinaldine is effected by anils formed by the condensation of aniline with either acetaldehyde or crotonaldehyde during the course of the reaction. This yields secondary amines as by-products these together with excess aniline are separated from the quinaldine by acetylation of the reaction mixture. The acetylated primary and secondary amines thus formed are less steam volatile than quinaldine which forms the basis of the isolation of the latter. 

This is an example of the Doebner synthesis of quinoline-4-carboxylic acids (cin-choninic acids), which consists of the condensation of a primary aromatic amine with pyruvic acid and an aldehyde. The mechanism is probably similar to the synthesis of quinolines discussed above and involves the intermediate formation of a dihydroquinoline derivative, which is subsequently dehydrogenated by the anils derived from the aromatic amine and the aldehyde. 

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