Preparation of Butyl Bromides

Place the reagents except the sulfuric acid in an eight-inch test tube. Add the sulfuric acid slowly, and cool the tube. Fit the top 

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The preparation of -butyl bromide as an example of ester formation by Method 1 (p. 95) has certain advantages over the above preparation of ethyl bromide. -Butanol is free from Excise restrictions, and the -butyl bromide is of course less volatile. and therefore more readily manipulated without loss than ethyl bromide furthermore, the n-butyl bromide boils ca. 40° below -butyl ether, and traces of the latter formed in the reaction can therefore be readily eliminated by fractional distillation. 

Run off the lower layer of bromide, dry it with calcium chloride (as in the above preparation of ethyl bromide) and finally distil the filtered bromide from a small flask, preferably through a short column. Collect the n-butyl bromide as a colourless liquid of b.p. 99-102°. Yield, 30 g. 

To a mixture of 0.10 mol of 1-ethoxy-l,2-heptadiene (see this chapter, Exp. 13) and 120 ml of diethyl ether was added 1 g of copper(I) bromide. A solution of butyl magnesium bromide in about 200 ml of diethyl ether, prepared from 0.25 mol of butyl bromide (see Chapter II, Exp. 5) was added in 15 min. The reaction was weakly exothermic and the temperature rose slowly to about 32°C. The mixture was held for an additional 40 min at that temperature, then the black reaction mixture was... 

B. 3-Methylheptanoic acid. In a 2-1. three-necked flask fitted with a mercury-sealed stirrer, a reflux condenser carrying a calcium chloride tube, and a dropping funnel are placed 25.0 g. (1.04 g. atoms) of magnesium turnings. The flask is heated to about 100° for a few minutes and then cooled to room temperature. A solution of 178 g. (1.30 moles) of -butyl bromide in 300 ml. of dry ether is prepared and of this solution about 10 ml., together with 30 ml. of dry ether, is run into the flask. The reaction is started by heating to reflux for a few seconds, the stirrer is started, and the remainder of the bromide solution is added at such a rate as to maintain constant reflux (about 1 hour). 

After the preparation of phenylmagnesium bromide is complete, the ethereal solution is cooled in an ice bath and 200 ml. of anhydrous ether is added. A solution of 58.3 g. (0.3 mole, 39.0 ml.) of feri-butyl perbenzoate (Note 1) in 120 ml. of anhydrous ether is added, dropwise, with stirring over a 30-minute period, and the stirring is continued for an additional 5 minutes. 

The use of a modified sodium bromide-sulfuric acid method for the preparation of alkyl bromides is described in connection with the preparation of ra-butyl bromide. This method has been used also for the preparations of iso-amyl and trimethylene bromides, but, in general, the yields were found to be somewhat lower than those obtained with the hydrobromic-sulfuric acid method. 

SAMPLE SOLUTION (a) The Gabriel synthesis is limited to preparation of amines of the type RCH2NH2, that is, primary alkylamines in which the amino group is bonded to a primary carbon. Butylamine may be prepared from butyl bromide by this method. 

To 250 g of 48 per cent hydrobromic acid contained in a 500-ml round-bottomed flask add 75 g (41 ml) of concentrated sulphuric acid in portions with shaking some hydrogen bromide may be evolved. Add 88 g (110 ml, 1.2 mol) of butan-l-ol, followed by 60 g (32.5 ml) of concentrated sulphuric acid in several portions with shaking, and finally a few chips of porous porcelain. Attach a reflux condenser to the flask and reflux the mixture gently on a wire gauze for 2-3 hours during this period the formation of butyl bromide is almost complete and a layer separates above the acid (1). If the preparation is carried out in the open laboratory, fit an absorption device (Fig. 2.61(a) or (b)) to the top of the condenser in order to absorb any hydrogen bromide and sulphur dioxide which may be evolved. Allow the contents of the flask to cool, remove the condenser and set it for downward distillation. Distil the mixture until no more oily drops of butyl bromide pass over (30-40 minutes). Transfer the distillate to a separatory funnel and remove the halide which... 

Cognate preparations. s-Butyl bromide (2-bromobutane). The quantities required are as for butyl bromide but with butan-2-ol (b.p. 99-100 °C) replacing the butan-l-ol. Two to three washings with concentrated hydrochloric acid are necessary, i.e. until the volume of the acid layer remains unchanged on shaking with halide. The yield of s-butyl bromide, b.p. 90.5-92.5 °C, is 150 g (92%). 

Cognate preparation. Butane-1-thiol. Use 51 g (40 ml, 0.372 mol) of butyl bromide (Expt 5.54), 38 g (0.5 mol) of thiourea and 25 ml of water. Reflux, with stirring, for 3 hours the mixture becomes homogeneous after 1 hour. Allow to cool and separate the upper layer of the thiol (A). Acidify the aqueous layer with a cold solution of 7 ml of concentrated sulphuric acid in 50 ml of water, cool and saturate with salt remove the upper layer of butane-1-thiol (B) and combine it with (A). Extract the aqueous liquid with 75 ml of ether, dry the ethereal extract with sodium sulphate or calcium sulphate and distil off the ether from a water bath through a fractionating column. Combine the residue with A) and (B), and distil. Collect the butane-1-thiol at 97-99 °C. The yield is 24 g (72%). 

Cognate preparations. Butyl 2-mtrophenyl ether (o-Butoxynitrobenzene). Place a mixture of 28 g (0.2 mol) of o-nitrophenol (Expt 6.102), 28 g (0.2 mol) of anhydrous potassium carbonate, 30g (23.5 ml, 0.22 mol) of butyl bromide and 200 ml of dry acetone in a 1-litre round-bottomed flask fitted with an efficient reflux condenser, and reflux on a steam bath for 48 hours. Distil off the acetone, add 200 ml of water and extract the product with two 100 ml portions of benzene (CAUTION). Wash the combined benzene extracts with three 90 ml portions of 10 per cent sodium hydroxide solution, remove the benzene by distillation at atmospheric pressure and distil the residue under reduced pressure. Collect the o-butoxynitrobenzene at 171-172°C/19mmHg (or at 127-129 °C/2mmHg) the yield is 30 g (77%). 

Butyl azodiformate, 44,18 a-Butyl bromide, preparation of -butyl Grignard reagent from, 41, 61 (-Butyl carbazate, 44, 20 conversion to (-butyl azidoformate, 44,15... 

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