Monomethylations

Homologous mono-alkyl ethers of ethylene glycol, such as monoethyl glycol (or 2-ethoxyethanol), HOC2H4OC2H5, form excellent solvents as they combine to a large extent the solvent properties of alcohols and ethers. The monoethyl and the monomethyl members have the technical names of ethyl cellosolve and methyl cellosolve respectively. Dioxan... 

Tertiary amines containing one alkyl and two aryl groups, such as mono-I ncthyldiphenyhiniir.e, Cl l3(C, l l.diX , arc rarely encountered and arc unimportant. They usually react with nitrous acid with the insertion of a nitroso group into only one of the two available para positions monomethyl-diphenylamine thus gives monomethyl-mono - pnitroso-diphenylamine. Cl hj(C.ill .)N C l 1 jXO, or V-nicthyl-p-nitrosodiphcnylaniine. 

B) Secondary amines, (i) Aromatic amines. Monomethyl and monoethylaniline, diphenylamine. (ii) Aliphatic and other amines. Diethyhmine, di-n-propylamine, di-isopropylamine. Also piperidine piperazine diethylene-diamine). 

Note on the laboratory preparation of monoethylaniline. Although the laboratory preparation of monomethyl- or monoethyl-aniline is hardly worth whUe, the following experimental details may be useful to those who wish to prepare pure monoethylaniline directly from amline. In a flask, fitted with a double surface reflux condenser, place 50 g. (49 ml.) of aniline and 65 g. of ethyl bromide, and boU gently for 2 hours or until the mixture has almost entirely sohdified. Dissolve it in water and boil off the small quantity of unreacted ethyl bromide. Render the mixture alkaUne with concentrated sodium hydroxide solution, extract the precipitated bases with three 50 ml. portions of ether, and distil off the ether. The residual oil contains anihne, mono- and di-ethylaniline. Dissolve it in excess of dilute hydrochloric acid (say, 100 ml. of concentrated acid and 400 ml. of water), cool in ice, and add with stirring a solution of 37 g. of sodium nitrite in 100 ml. of water do not allow the temperature to rise above 10°. Tnis leads to the formation of a solution of phenyl diazonium chloride, of N-nitrosoethylaniline and of p-nitrosodiethylaniline. The nitrosoethylaniline separates as a dark coloured oil. Extract the oil with ether, distil off the ether, and reduce the nitrosoamine with tin and hydrochloric acid (see above). The yield of ethylaniline is 20 g. 

The desired pyridylamine was obtained in 69 % overall yield by monomethylation of 2-(aminomethyl)pyridine following a literature procedure (Scheme 4.14). First amine 4.48 was converted into formamide 4.49, through reaction with the in situ prepared mixed anhydride of acetic acid and formic acid. Reduction of 4.49 with borane dimethyl sulfide complex produced diamine 4.50. This compound could be used successfully in the Mannich reaction with 4.39, affording crude 4.51 in 92 % yield (Scheme 4.15). Analogous to 4.44, 4.51 also coordinates to copper(II) in water, as indicated by a shift of the UV-absorption maximum from 296 nm to 308 nm. 

Davies and Warren have investigated the nitration of naphthalene, ace-naphthene and eight dimethylnaphthalenes in acetic anhydride at o °C. Rates relative to naphthalene were determined by the competition method, and the nitro-isomers formed were separated by chromatographic and identified by spectrophotometric means. The results, which are summarised in the table, were discussed in terms of various steric effects, and the applicability of the additivity rule was examined. For the latter purpose use was made of the data of Alcorn and Wells (table 10.2) relating to the nitration of monomethyl-naphthalenes at 25 °C. The additivity rule was found to have only limited utility, and it was suggested that the discrepancies might be due in part to the... 

A special problem arises in the preparation of secondary amines. These compounds are highly nucleophilic, and alkylation of an amine with alkyl halides cannot be expected to stop at any specifle stage. Secondary amides, however, can be monoalkylated and lydrolyzed or be reduced to secondary amines (p. 11 If.). In the elegant synthesis of phenyl- phrine an intermediate -hydroxy isocyanate (from a hydrazide and nitrous acid) cyclizes to pve an oxazolidinone which is monomethylated. Treatment with strong acid cleaves the cyclic irethan. 

TABLE 1-16 ULTRAVIOLET ABSORPTION SPECTRA OF THIAZOLE AND ITS MONOMETHYL DERIVATIVES... 

The normal boiling point of 2-methylthiazole is 17 0= 128.488 0.005°C. The purity of various thiazoles was determined cryometrically by Handley et al. (292), who measured the precise melting point of thiazole and its monomethyl derivatives. Meyer et al. (293, 294) extended this study and, from the experimental diagrams of crystallization (temperature/degree of crystallization), obtained the true temperatures of crystallization and molar enthalpies of fusion of ideally pure thiazoles (Table 1-43). 

The polymeric products can be made to vary widely in physical properties through controlled variation in the ratios of monomers employed in thek preparation, cross-linking, and control of molecular weight. They share common quaHties of high resistance to chemical and environmental attack, excellent clarity, and attractive strength properties (see Acrylic ester polymers). In addition to acryHc acid itself, methyl, ethyl, butyl, isobutyl, and 2-ethylhexyl acrylates are manufactured on a large scale and are available in better than 98—99% purity (4). They usually contain 10—200 ppm of hydroquinone monomethyl ether as polymerization inhibitor. 

The esters are produced in minimum purity of 99.5%. The yield, based on acryflc acid, is in the range of about 95—98% depending on the ester and reaction conditions. Monomethyl ether of hydroquinone (10—100 ppm) is added as polymeri2ation inhibitor and the esters are used in this form in most... 

Acryhc acid and esters are stabilized with minimum amounts of inhibitors consistent with stabihty and safety. The acryhc monomers must be stable and there should be no polymer formation for prolonged periods with normal storage and shipping (4,106). The monomethyl ether of hydroquinone (MEHQ) is frequentiy used as inhibitor and low inhibitor grades of the acrylate monomers are available for bulk handling. MEHQ at 10—15 ppm is generally... 

In normal practice, inhibitors such as hydroquinone (HQ) [123-31 -9] or the monomethyl ether of hydroquinone (MEHQ) [150-76-5] are added to acrylic monomers to stabilize them during shipment and storage. Uninhibited acrylic monomers should be used prompdy or stored at 10°C or below for no longer than a few weeks. Improperly iahibited monomers have the potential for violent polymerizations. HQ and MEHQ require the presence of oxygen to be effective inhibitors therefore, these monomers should be stored in contact with air and not under inert atmosphere. Because of the low concentration of inhibitors present in most commercial grades of acrylic monomers (generally less than 100 ppm), removal before use is not normally required. However, procedures for removal of inhibitors are available (67). 

Acrylonitrile will polymerize violendy in the absence of oxygen if initiated by heat, light, pressure, peroxide, or strong acids and bases. It is unstable in the presence of bromine, ammonia, amines, and copper or copper alloys. Neat acrylonitrile is generally stabilized against polymerization with trace levels of hydroquinone monomethyl ether and water. 

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