Urethanes, hydrolysis preparation

The above procedure describes the only known preparation of the inner salt of methyl (carboxysulfamoyl)triethylammonium hydroxide and illustrates the use of this reagent to convert a primary alcohol to the corresponding urethane. Hydrolysis of the urethane would then provide the primary amine. The method is limited to primary alcohols secondary and tertiary alcohols are dehydrated to olefins under these conditions, often in synthetically useful yields. ... 

The Cunius degradation of acyl azides prepared either by treatment of acyl halides with sodium azide or trimethylsilyl azide [47] or by treatment of acyl hydrazides with nitrous acid [f J yields pnmarily alkyl isocyanates, which can be isolated when the reaction is earned out in aptotic solvents If alcohols are used as solvents, urethanes are formed Hydrolysis of the isocyanates and the urethanes yields primary amines. 

Early attempts to prepare 5-amino- and 5-acylaminobenzofuroxans by hypochlorite oxidation of the corresponding o-nitroanilines met with failure. Pyrolysis of the appropriate azide, however, gives 5-dimetliylamino- and 5-acetamidobenzofuroxan, whereas urethans of type (33) are produced by Curtius degradation of the 5-carboxylic acid. Controlled hydrolysis of the acetamido compound and the... 

In a specific example of adhesive bonds between cold rolled steel and SMC adherends (Table II) an adhesive based on hydrolysis resistant epoxy chemistry (i.e., adhesive E) was compared with an adhesive based on hydrolysis prone urethane chemistry (i.e., adhesive C) in composite to cold rolled steel bonds. After corrosion testing, a significant difference in both retention of initial bond strength and locus of failure was observed. For bonds prepared with adhesive E, little if any reduction of the initial bond strength was observed after corrosion testing. The locus of failure for both the tested and untested bonds was largely in the... 

The instability of primary nitramines in acidic solution means that the nitration of the parent amine with nitric acid or its mixtures is not a feasible route to these compounds. The hydrolysis of secondary nitramides is probably the single most important route to primary nitramines. Accordingly, primary nitramines are often prepared by an indirect four step route (1) acylation of a primary amine to an amide, (2) A-nitration to a secondary nitramide, (3) hydrolysis or ammonolysis with aqueous base and (4) subsequent acidification to release the free nitramine (Equation 5.17). Substrates used in these reactions include sulfonamides, carbamates (urethanes), ureas and carboxylic acid amides like acetamides and formamides etc. The nitration of amides and related compounds has been discussed in Section 5.5. 

Hydrolysis of the trimethylsilyl urethane (1 R=C02SiMe3), prepared by the action of trimethylsilyl iodide on the methyl carbamate (1 R = C02Me), with methanol at -78 °C yields the carbamic acid (1 R = C02H). On allowing a CDC13 solution of the carbamic acid to warm to room temperature, decarboxylation takes place to yield the deep red, highly unstable 1//-azepine (1 R=H) (80AG(E)1016>. 

This is a powerful explosive, stronger than tetryl but weaker than cyclonite. It is, however, of no practical value chiefly because its preparation is too expensive, requiring first the conversion of methylamine into urethane and then into its nitro derivative. On hydrolysis the latter yields methylnitramine. Similarly, the hydrolysis of dinitrodimethyloxamide (p. 35) leads to the formation of methylnitramine. 

Treatment of 2-lithiofurans with ethyl borate and hydrolysis of the resultant boronic ester yields 2(3//)-furanones (69AK(29)229). 2,5-Dimethyl-3(2i/)-furanone (358) has been prepared by a Curtius reaction on the ester (359) and acid hydrolysis of the intermediate urethane (360) (Scheme 97). This type of reaction has been used to synthesize muscarine and its stereoisomers (61QR153). 

Thus, the N-protected indoline 211 (Scheme 33), on regiospecific metallation followed by bromination with dibromotetrafluoroethane provided the 7-bromoindoline 212. Removal of the urethane functionality and subsequent benzylation of the free amine formed, furnished the tertiary amine 213. Addition of oxazoline 214 derived from 2,4,5-trimethoxybenzaldehyde to the Grignard reagent prepared from 213, followed by acid hydrolysis of the resulting biaryl 215 afforded the 2-substituted isobutylbenzoate 216. Catalytic N-debenzylation of the methylester 217 obtained by transesterification of 216 yielded oxoassoanine (203). 

Z-Menthyl Isocyanate. Pickard and Littlebury 20-21 found that Z-menthyl isocyanate forms crystalline esters (urethanes) with many alcohols and phenols. The two diastereoisomeric urethanes from cZZ-l-phenyl-1-p-hydroxyphenylethane and from dZ-oc-tetrahydro-/3-naphthol were separated readily.2 The method has not been applied widely. Z-Men-thyl isocyanate is the most readily available resolving agent of this type but is difficult to prepare. The urethanes are not easily hydrolyzed, and the isocyanate is not recovered in the hydrolysis but is converted to the amine. 

Lithium aluminium hydride reduction of 235 followed by mesylation afforded 236. The latter was oxidized with osmium tetroxide and sodium metaperiodate to yield the cyclobutanone 237. Treatment of 237 with acid afforded in 48% yield the ketoacid (238), which was esterified with diazomethane to 239. The latter was converted to the ketal 240 by treatment with ethylene glycol and /7-toluenesulfonic acid. Compound 240 was reduced with lithium aluminium hydride to the alcohol 241. This alcohol had been synthesized previously by Nagata and co-workers (164) by an entirely different route. The azide 242 was prepared in 80% yield by mesylation of 241 and treatment of the product with sodium azide. Lithium aluminium hydride reduction of 242 gave the primary amine, which was converted to the urethane 243 by treatment with ethyl chloroformate. The ketal group of 243 was removed by acidic hydrolysis and the resulting ketone was nitro-sated with N204 and sodium acetate. Decomposition of the nitrosourethane with sodium ethoxide in refluxing ethanol afforded the ketone 244 in 65% yield. The latter had been also synthesized previously by Japanese chemists (165). The ketone 244 was converted to the ketal 246 and the latter to 247... 

Trimethyl-D-arabofuranose (XXV) has been prepared by the degradation of 2,3,4,6-tetramethyl-D-gluconamide (XXIII) by the action of sodium hypochlorite (Weerman reaction), the cyclic urethane (XXIV) undergoing hydrolysis with dilute sodium hydroxide solution in the cold.80... 

The Curtius reaction of l,2,5-thiadiazole-3-carbohydrazide (79) proceeded normally and in high yield to the ethyl urethane (80, R = Et). The ethyl urethane, however, resisted acid hydrolysis and was extensively decomposed by base. The benzyl urethane (80, R = CH2Ph), on the other hand, was smoothly hydrolyzed to the amine with aqueous acid. Attempts to prepare 1,2,5-thiadiazole-3,4-dicarboxazide from the dihydrazide resulted in an unstable product which exploded violently. ... 

The procedure given above is essentially the method of Thiele. Methylhydrazine has also been prepared by reduction and subsequent hydrolysis of nitrosomethylurea, nitromethyl-urethane, and nitrosomethylamine sulfonic acid and by methylation of hydrazine hydrate with methyl iodide or diazomethane. ... 

Polyether Polyols. The major polyols for preparing various urethane foams are polyether polyols. Polyester polyols are used only in specific applications. The advantages of polyether polyols are choice of functionality and equivalent weight the viscosities are lower than those of conventional polyesters production costs are cheaper than for aliphatic polyesters and resulting foams are hydrolysis-resistant. 

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