1.2- Dibromoethyl ethyl ether

Dibromoethyl ethyl ether 531 Dry HC1 is led cautiously into a mixture of paraldehyde (100 g) and ethanol (100 g) which is cooled in a freezing mixture. Two layers are formed, the upper of which is dried over CaCl2 and fractionated (69% b.p. 93-96°). To this 1-chloro-ethyl ethyl ether is added the theoretical quantity of bromine, portionwise (with time for decolorization in each case), with cooling in ice HC1 is evolved. When the crude dibromo product is distilled in a vacuum it has b.p. 92-95°/17 mm, the yield being 88-91 %. 

From saturated halogen compounds removal of the first molecule of hydrogen halide, to form an ethylenic linkage, is considerably easier than removal of the second, to form the triple bond. For example, in the preparation of ethoxyacetylene CH=COC2H5 from 1,2-dibromoethyl ethyl ether the first molecule of hydrogen bromide can be removed by diethylaniline, but the second only by potassium hydroxide in a vacuum.179... 

D. a-Allyl- -bromoelhyl ethyl ether. The same apparatus is used as in the preparation of allylmagnesium bromide. The flask is charged with an amount of the Grignard solution (part C) equivalent to 2.78 moles of allylmagnesium bromide (or chloride) and cooled in an ice bath. A solution of 580 g. (2.5 moles) of o , 3-dibromoethyl ethyl ether (part B) in an equal volume of anhydrous ether is added slowly with stirring over a period of 3-4 hours. The mixture is allowed to stand overnight and is then hydrolyzed with 75 ml. of 20% acetic acid followed by 500 ml. of water. The ether layer is separated, washed with four 100-ml. portions of 10% aqueous sodium bicarbonate solution followed by four 100-ml. portions of saturated aqueous sodium chloride solution, dried over 100 g. of anhydrous calcimn sulfate, and distilled under reduced pressure. The yield of colorless a-allyl-/3-bromoethyl ethyl ether is 370-396 g. (77-82% based on the a, 3-dibromoethyl ethyl ether), b.p. 72-75°/21 mm., 1.4600-1.4606. 

Distillation is required to remove aldehyde, alcohol, and water which would react with the Grignard reagent in the next step. a,d-Dibromoethyl ethyl ether is also a lachrymator. 

Ethoxyacetylene has been prepared from /3-bromovinyl ethyl ether and potassium hydroxide in 50-55% yield 6 from a,/3-di-bromoethyl ethyl ether and potassium hydroxide 6 and from diethyl chloroacetal, diethyl bromoacetal, a,/3-dichloroethyl ethyl ether, or a,/3-dibromoethyl ethyl ether and sodium amide.10... 

Dibromocyclohexanone, 32, 38 Dibromoethyl ethyl ether, 36, 61 10,11-Dibromohendecanoicadd, 32,105 Dibromomalononitrile-potassium... 

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). 

Several significant pyrrole syntheses involve the formal tricomponent cyclization of type III ace (equation 126). The Hantzsch pyrrole synthesis involves a dicarbonyl compound, an a -halo ketone and ammonia or an amine. The mechanistic pattern is similar to that involved in the Knorr synthesis (Section 3.06.3.4.1). In addition to a-halo ketones and a-haloal-dehydes, compounds such as 1,2-dichloroethyl acetate, 1,2-dibromoethyl acetate and 1,2-dichloroethyl ethyl ether can serve as a -haloaldehyde equivalents (equation 127) (70CJC1689, 70JCS(C)285>. It is believed that the initial step in these reactions is the formation of a stabilized enamine from the amine and the /3 -dicarbonyl compound. A structural ambiguity... 

Dibromoethyl silicon dichloride, (CH2Br.CH2)2SiCl2, is produced by heating together a mixture of two molecular proportions of ethylene bromide with 1 mol. of silicon tetrachloride dissolved in ether, and four molecular proportions of sodium and a little ethyl acetate. The product is a dark brown oil. Doubt has recently been expressed as to the existence of this compound. ... 

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