Carbonium reactions with amine

CgH5Cr(CO)3 group is relatively small, but it is sufficient to produce noticeable changes in reactivity. Benzyl chloride and its complex (PhCH2Cl)Cr(CO)3 are both solvolysed by an SJ. mechanism in ethanol in which the carbonium ion is an intermediate. It has been found that the complex reacts about 10 faster than the free halide. These effects have been exploited in organic synthesis. Complexed benzyl alcohols can be converted into ethers or amines by reaction with hexafluorophosphoric acid followed by an alcohol or an amine. The Ritter reaction, which involves electrophilic addition to a nitrile, is also greatly accelerated. While an uncomplexed benzyl alcohol requires over a day for complete reaction, the complex reacts within a few minutes. 

Apparently the alkoxy radical, R O , abstracts a hydrogen from the substrate, H, and the resulting radical, R" , is oxidized by Cu " (one-electron transfer) to form a carbonium ion that reacts with the carboxylate ion, RCO - The overall process is a chain reaction in which copper ion cycles between + 1 and +2 oxidation states. Suitable substrates include olefins, alcohols, mercaptans, ethers, dienes, sulfides, amines, amides, and various active methylene compounds (44). This reaction can also be used with tert-huty peroxycarbamates to introduce carbamoyloxy groups to these substrates (243). 

S-Protonated Aryliminium Salts Hesse has made a much more extensive study of the reaction of aryl primary amines (58) with higher aldehydes (see 59) and a suitable alkene, usually styrene or a-methylstyrene, and found that high yields of tetra-hydroisoquinoline (60) could be obtained even when an electron-withdrawing group was present in the aryl ring. Carbonium ion (61) appeared likely as an intermediate. 

Liquid ammonia can be used as a solvent in the anionic polymerization of styrene initiated chemically (15). Moreover, the basic nature of ammonia and amines needs no further justification. These data appear to lead to the tentative conclusion that the growing species in these systems is the positively charged carbonium ion, which may terminate with ammonia (and amines) either by a proton transfer mechanism or an addition reaction to form a nonpolymerizing ammonium ion (8)—viz.,... 

Assuming a single-ion (carbonium ion) propagation step and based on scavenger studies with ammonia and amines and on electrical conductance measurements, rate constants for the propagation reaction (ion-molecule reaction) can be estimated. These estimates are free of the correction that one has to apply (or ignore) for chemically generated ion pair ionic polymerization, but are subject to other limitations imposed by different assumptions in the treatment of the data. 

The biomimetic construction of piperidine skeletons from N-methylhomoallyl-amines is performed by means of the ruthenium-catalyzed oxidation and subsequent olefm-iminium ion cyclization reaction. trans-l-Phenyl-3-propyl-4-chloropiper-idine 57 ivas obtained from N-methyl-N-(3-heptenyl)aniline stereoselectively via 56 upon treatment ivith a 2 N HCI solution (Eq. 3.72). This cyclization is the first demonstration of biomimetic formation of piperidine structure using N-methyl group, and can be rationalized by assuming the formation of iminium ion 58 by protonation of the oxidation product 56, subsequent elimination of f-BuOOH, nucleophilic attack of an alkene, giving a carbonium ion, which is trapped with Cl nucleophile from the less hindered side. 

Nitrous acid with the chemical formula 11N()> is unstable, and therefore usually a mixture of NaNO and so dilute hydrochloric acid or sulfuric acid is used to produce nitrous acid indirectly. Primary ahphatic amines with nitrous acid give very imstable diazonium salts which spontaneously decompose by losing N2 to form a carbonium ion. The carbonium ion goes on to produce a mixture of alkenes, alkanols or alkyl halides, with alkanols as the major product. This reaction is of Ittle synthetic importance because the diazonium salt formed is too unstable, even under quite cold conditions. 

The problem now is to determine whether R is alkyl or aryl. It is known that primary aliphatic amines yield unstable diazonium compounds that immediately decompose to give nitrogen (N2) gas and a carbonium ion. The problem indicates that nitrogen gas is formed but only after a gradual warming to room temperature. It is known that primary aromatic amines (that have formed the diazonium compound) will yield the phenol under such conditions with the evolution of nitrogen gas. Hence, the only conclusion is that the unknown amine must be aromatic, since the reaction of the diazonium is gradual, not immediate. 

---