Methyl cations amines

Keywords methyl cations, amines, ion-molecule reactions... 

The nature of the intermediate cationic species, whether it is a classical methyl cation or a nonclassical bridged cation, has also been determined. The deamination of optically active e c/o-2-aminobicyclo[2.2.1]hcplane-exo-2-carbonitrile gave 2-hydroxybicyclo[3.1. l]-heptane-1-carbonitrile (19) in 9% yield with 92% retention of the optical activity. Similarly, deamination of e.vo-2-trifluoromethylbicyclo[2.2.1]heptyl-e Jo-2-amine gave 1-trifluoromethyl-bicyclo[3.1.1]heptan-2-ol (20) in 11 % yield with 88% retention of the optical activity. These results are interpreted in terms of intermediate bridged cations.87... 

Inorganic bases have been also employed in this system. When Butcher first used alkali carbonates [50], it was reported that, in DMF and at ambient temperature, the carbamation of primary and secondary aliphatic amines (or also arylamines) with alkyl halides under a C02 atmosphere (0.1 MPa) was effectively promoted by Cs2C03 [50, 51]. The Cs+ cations in the solvent used (DMF) did not form ion pairs with counterions, and favored the formation of naked carbamate anions that were more reactive at the O-ends with alkyl halides. Jung further found that the addition of tetrabutylammonium iodide (TBAI) to the system RR NH/ C02/RX/Cs2C03/DMF promoted the carbamation process with a higher yield and selectivity with respect to N-alkylation [51]. The process has been successfully extended to the synthesis of carbamate functionalities on solid phases. In this case, resin-bound carbamates are readily released from the resin by treatment with LiAlH4 in THF, yielding the respective N-methyl secondary amines [51]. 

The much more highly charged silicon atom can interact far more readily with nucleophiles. Silyl cations may even be complexed simultaneously and symmetrically by two electron pair donors (hypercoordination), in contrast to carbocations. With ammonia, the methyl cation gives the very stable protonated methyl amine, H3C-NH3 a second ammonia molecule is only weakly bound to this complex. If both NH3 groups are forced to be equidistant from carbon, a Sn2 transition state results, 20 kcal mol" higher in energy than the minimum. 

When chloroprene was grafted onto cationic aminated starch, a latex was obtained that imparted wet strength to paper and also served as a pressureless adhesive for wood 2951 Starch dialdehyde when grafted with acrylonitrile, methyl methacrylate, or both, produced a biodegradable filler for poly (vinyl chloride) plastics.2942 Starch xanthates grafted with vinyl monomers were also used to produce additives for reinforced foamed rubber.2944,2945... 

Vinyl amines (also called enamines) are even more reactive than vinyl ethers toward electrophiles. The qualitative nature of the conjugation is the same as in vinyl ethers, both for the neutral vinyl amine and for the cationic intermediate. However, nitrogen is an even better electron donor than oxygen, so the stabilizing effect is stronger. The stabilization for the cation is calculated to be around 80 kcal/mol relative to the methyl cation. 

A detailed laser flash photolysis study of the reactions of the 4-methoxystyrene radical cation and its P-methyl and p.p-di-methyl analogs with amines and pyridines in acetonitrile and aqueous acetonitrile has been carried out. " Representative kinetic data are summarized in Table 6 and cover approximately 4 orders of magnitude in time scale. A combination of transient spectra, product studies, and redox potentials has been used to establish which of the three possible reactions contributes to the measured rate constant for any given radical cation/amine pair. For example, transient spectra obtained after quenching of the radical cations with either DABCO or aniline clearly show the formation of the amine radical cation, consistent with the fact that both of these amines have substantially lower oxidation potentials than any of the three styrenes. Reaction with primary amines occurs by addition, as evidenced by the formation of a transient in the 300-nm region that is assigned to the substituted benzyl radical. These results are consistent with the high oxi-... 

Control of reactivity by activating a strong stereoelectronic effect The differences in the donor ability of heteroatoms can be used in a variety of ways. For example, it leads to a convenient synthesis of diaza[4] helicenes from tris(2,6-dimethoxyphenyl)methyl cation and primary amines (Figure 10.21). Again, the transformation is driven by favorable thermodynamics originating from a delocalizing donor-acceptor interaction between nitrogen lone pairs and benzylic cations. 

Gas-Phase Reactions of Free Methyl Cations with Amines and Their Organosilicon Analogues A Radiochemical Study... 

Summary Reactions of free methyl cations with diisobutylamine (1), isobutylaminotrimethylsilane (2) and hexamethyldisilazane (3) were studied by the radiochemical method. It was shown that in all cases studied, the proton transfer is a predominant channel. Probabilities for the reaction to enter this channel are 0.87 for 1, 0.67 for 2 and 0.93 for 3. The last value contradicts the well-known dependence of the lowering of the proton affinity of amines upon the CHa/SiHa ratio. However, quantum chemical calculations have shown that the interaction of the silazane HOMO with the CHa LUMO is symmetry forbidden. This fact may result in the lowering of the methyl cation affinity for silazanes and preference for the proton transfer channel. 

Assuming similar mechanisms for the reactions of methyl cations with amines and with their... 

Scheme 1. The mechanism of the reaction of free methyl cations with amines R1NHR2 (Ri = R2 = iBu R = iBu,...

The radiochromatographic analysis of the products of reactions of methyl cations with diisobutylamine, isobutylaminotrimethylsilane and hexamethyldisilazane has shown that the reaction mechanism which includes two competitive channels is also operative in the case of organosilicon amines. 

The substitution of the alkyl groups in amines by silyl groups decreases their proton affinity [6] and, as a result, the proton transfer reactions from the methyl cation are less competitive with condensation. Indeed, the probability of proton transfer decreases in going from diisobutylamine to isobutylaminotrimethylsilane. However, in the case of hexamethyldisilazane this rule is broken. 

Alkylations of aromatic amines can be satisfactorily achieved with stable carbonium ions, even in the presence of high concentrations of mineral or Lewis acid catalysts. The diphenylmethyl and triphenyl-methyl cations have been shown to attack predominantly at the para position of anilines and the prominent features of these re-... 

Squaric dithiones (16 X = S) react with an amine to give transamination with intramolecular migration of a sulphur atom. -Methylated cations are obtained with methyl fluorosulphonate, and on hydrolysis lose a dimethylamino-group to give a ketone. Reactions of a cyclobutenedithione with a thiocyanate and reaction of a monothiosquarate dianion have been reported. 

Chem. Descrip. Methyl dioctadecyl amine Ionic Nature Cationic... 

Ethylene oxide adds to the bis(2-hydtoxyethyl) teitiaiy amine in a random fashion where x y y = n y2. Ethoxylated amines, varying from strongly cationic to very weakly cationic in character, are available containing up to 50 mol of ethylene oxide/mol of amine. Ethyoxylated fatty amine quaternaries, cationic surfactants (both chloride from methyl chloride and acetate from acetic acid), ate also available. 

Tertiary Amine-Containing Copolymers. Copolymers based on DMAEMA (dimethylarninoethyl methacrylate) in either free amine form or quatemized with diethyl sulfate or methyl chloride have achieved commercial significance as fixatives in hair-styling formulations, especially in the weU-pubhcized "mousses" or as hair-conditioning shampoo additives. This success has occurred because the cationic charge affords substantive resins that strongly adhere to the hair (141). 

---