Ethanol with hydrogen bromide

The gas phase reaction of ethanol with hydrogen bromide can occur either by elimination or substitution. 

Esters of diphenylacetic acids with derivatives of ethanol-amine show mainly the antispasmodic component of the atropine complex of biologic activities. As such they find use in treatment of the resolution of various spastic conditions such as, for example, gastrointestinal spasms. The prototype in this series, adiphenine (47), is obtained by treatment of diphenyl acetyl chloride with diethylaminoethanol. A somewhat more complex basic side chain is accessible by an interesting rearrangement. Reductive amination of furfural (42) results in reduction of the heterocyclic ring as well and formation of the aminomethyltetrahydro-furan (43). Treatment of this ether with hydrogen bromide in acetic acid leads to the hydroxypiperidine (45), possibly by the intermediacy of a carbonium ion such as 44. Acylation of the alcohol with diphenylacetyl chloride gives piperidolate (46). ... 

Hydrolysis, of 2 benzyl 2 carbometh oxycyclopentanone with lithium iodide m 2,4 6-colhdme, 46, 7 of 7 butyrolactone to ethyl y-bromo-butyrate with hydrogen bromide and ethanol, 46, 42 of 2,5 dicarbethoxy 1 4-cyclohexane-dione to 1,4 cyclohexanedione, 46, 25... 

We have mentioned earlier that when ethanol reacts with hydrogen bromide, ethyl bromide is formed. Similar treatment of ethanol with hydrogen chloride or hydrogen iodide gives us the corresponding ethyl halides ... 

The structural homology between intermediate 4 and isostrych-nine I (3) is obvious intermediates 3 and 4 are simply allylic isomers and the synthetic problem is now reduced to isomerizing the latter substance into the former. Treatment of 4 with hydrogen bromide in acetic acid at 120°C results in the formation of a mixture of isomeric allylic bromides which is subsequently transformed into isostrychnine I (3) with boiling aqueous sulfuric acid. Following precedent established in 194810 and through the processes outlined in Scheme 8a, isostrychnine I (3) is converted smoothly to strychnine (1) upon treatment with potassium hydroxide in ethanol. Woodward s landmark total synthesis of strychnine (1) is now complete. 

Kaneko (28) followed essentially the method described by Prasad and Swan (25). The ketone XXVIIb was, however, prepared by a different route and its phenylhydrazone on heating with hydrogen bromide in ethanol yielded a bromine-containing product. This was first dehydrogenated with palladium charcoal in -cymene and subsequently de-brominated with palladium charcoal and hydrogen to form fiavopereirine. 

Chloropyrazine reacted with benzyl 7V-hydroxy-7V-phenylcarbamate [PhN(OH)-COOCHjPh] in ethanolic potassium hydroxide to give 5-(4 -benzyloxycarbonyl-aminophenyl)-2-hydroxypyrazine which with hydrogen bromide in acetic acid gave 5-(4 -aminophenyl)-2-hydroxypyrazine (990). 

Preparation (b). The reaction sequence is shown in the formulation. Treatment of paraldehyde and absolute ethanol with hydrogen chloride gas at —5° produces a-chloroethyl ethyl ether (1), which on bromination affords a,j8-dibromoethyl ethyl ether (2). Coupling with allylmagnesium bromide gives (3), which on reaction with zinc dust in n-butanol generates 1,4-pentadiene. Thus one double bond is that of allyl bromide, and the other is generated by elimination of BrOCjH, from the bromohydrin ethyl ether (3). 

In most of the reactions that we have described here, the substrate has been modified by reaction at the functional group, and the hydrocarbon framework has remained unchanged. In Example 2.1, ethanol reacted with hydrogen bromide at the site where the hydroxyl group is attached to produce bromoethane... 

Nucleophilic displacement. Ethanol, CzHgOH, a typical alcohol, reacts with hydrogen bromide to give ethyl bromide, C HtBr. Ethanol does not react with NaBr. (a) Why cannot Br replace OH (b) Suggest a mechanism for the reaction with HBr. (Hint Alcohols are weak bases.)... 

Bromoacetic acid can be prepared by the bromination of acetic acid in the presence of acetic anhydride and a trace of pyridine (55), by the HeU-VoUiard-Zelinsky bromination cataly2ed by phosphoms, and by direct bromination of acetic acid at high temperatures or with hydrogen chloride as catalyst. Other methods of preparation include treatment of chloroacetic acid with hydrobromic acid at elevated temperatures (56), oxidation of ethylene bromide with Aiming nitric acid, hydrolysis of dibromovinyl ether, and air oxidation of bromoacetylene in ethanol. 

To a solution of 30.7 g (0.203 mol) of 1-phenoxy-2-aminopropane in 150 ml of ethanol there was added 31.9 g (0.100 mol) of 1-(4 -benzyloxyphenyl)-2-bromopropanone-1. The mixture was heated to boiling temperature and the solution was then refluxed in a reflux condenser for 3 hours. Most of the ethanol was then distilled off in vacuo. Then to the residue there was added about 150 ml of diethyl ether. The hydrogen bromide salt of 1-phenoxy-2-aminopropane was filtered off and washed with diethyl ether. 

Interaction with water, methanol or ethanol is violent, hydrogen bromide being evolved. 

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