Dimethylamino groups

Figure B2.4.1. Proton NMR spectra of the -dimethyl groups in 3-dimethylamino-7-methyl-l,2,4-benzotriazine, as a fiinction of temperature. Because of partial double-bond character, there is restricted rotation about the bond between the dunethylammo group and the ring. As the temperature is raised, the rate of rotation around the bond increases and the NMR signals of the two methyl groups broaden and coalesce.

This preparation illustrates the use of dimethyl sulphate to convert a primary amino group into the secondary monomethylamino group, without the methy-lation proceeding to the tertiary dimethylamino stage. The methylation of anthranilic acid is arrested at the monomethylamino stage by using i-i molecular equiN alents of sodium hydroxide and of dimethyl sulphate. The reactions can be considered as ... 

The amino group is readily dia2oti2ed in aqueous solution, and this reaction forms a basis for the assay of sulfas. Aldehydes also react to form anils, and the yellow product formed with 4-(dimethylamino)hen2a1dehyde can be used for detection in thiu-layer and paper chromatography. Chromatographic retention values have been deterrnined in a number of thiu layer systems, and have been used as an expression of the lipophilic character of sulfonamides (23). These values have corresponded well with Hansch lipophilic parameters determined in an isobutyl alcohol—water system. 

Analytical and Test Methods. In addition to the modem spectroscopic methods of detection and identification of pyrroles, there are several chemical tests. The classical Runge test with HCl yields pyrrole red, an amorphous polymer mixture. In addition, all pyrroles with a free a- or P-position or with groups, eg, ester, that can be converted to such pyrroles under acid conditions undergo the Ehrlich reaction with p-(dimethylamino)henzaldehyde to give purple products. 

Tricyclic Antidepressants. Imipramine [50-49-7] (32), which was the first tricycHc antidepressant to be developed, is one of many useful psychoactive compounds derived from systematic molecular modifications of the antihistamine prometha2ine [60-87-7] (see Histamine and histamine antagonists). The sulfur atom of prometha2ine was replaced with an ethylene bridge and the dimethylamino group attached to an / -propyl group, rather than to an isopropyl one, of the side chain. The actual synthesis of (32) is typical of the compounds in this class (37). 

The basic piSTa values, which have to be considered as equilibrium values, including those of anhydrous and hydrated species, reveal a destabilizing inductive effect of the 6- and 7-methyl group towards 3,4-hydrate formation, as do also the 2-methylamino and 2-dimethylamino groups for additional steric reasons. If the cation of 2-aminopteridine did not add water its value would be about 1.6, arrived at by substracting from the piSTa 2.6 of the essentially anhydrous 2-amino-4,7-dimethylpteridine cation 0.3 for the 7- and 0.7 for the 4-methyl group. The difference between the observed value of 4.29 and the... 

Dimethylaminopyrazoles react with alkylating agents to afford quaternary salts (72BSF2807). The nitrogen atom of the dimethylamino group is the most reactive in the case of 3-dimethylamino- and 4-dimethylamino-pyrazoles (formation of 456 and 457 salts, respectively) whereas 5-dimethylaminopyrazoles yield aminopyrazolium salts (458). 

The dimethylamino group can be cleaved from a pyrrole in low yield with chro-mous acetate. 

The dimethylamino group rotation follows a first-order rate law the exehanging methyl protons show no eoupling and their singlet signals are of the same intensity. Under these eonditions, equation 7 affords the rate eonstant k,. at the eoaleseenee point ... 

Hence the activation energy barrier to dimethylamino group rotation in dimethylacetamide (41) is calculated from equation 9 with k,. = 17.8 at the coalescence point 353 K (Fig. 2.26) ... 

The two methyl groups are not equivalent at 303 K (3 = 2.86 and 3.14), rotation about the CN bond is frozen, because this bond has partial tt character as a result of the mesomerlc (resonance) effects of the dimethylamino group (+Af) and of the aldehyde function (-M), so that there are cis and trans methyl groups. Hence one can regard 3-(A(A -dlmethylamlno)acrolein as a vinylogue of dlmethylformamide and formulate a vlnylogous amide resonance. 

Finally from the logarithmic form of the Eyrlng equation, the free enthalpy of activation, AG, of rotation of the dimethylamino group at the coalescence temperature (318 K) can be calculated ... 

---