Org. Synth. 1935, 15, 24
DOI: 10.15227/orgsyn.015.0024
n-DODECYL BROMIDE
[Dodecane, 1-bromo-]
Submitted by E. Emmet Reid, John R. Ruhoff, and Robert E. Burnett.
Checked by W. H. Carothers and W. L. McEwen.
1. Procedure
In a 500-cc. distilling flask, fitted with a thermometer and an inlet tube leading to the bottom (Note 1), is placed 186 g. (1 mole) of n-dodecyl alcohol (Note 2). An adapter, one end of which is immersed in about 75 cc. of water contained in a 125-cc. Erlenmeyer flask, is attached to the side arm of the flask. All connections are of rubber. The alcohol is heated to 100°, and dry hydrogen bromide (Note 3) is passed in at 100–120° (Note 4) until no more absorption occurs (Note 5). The crude bromide, together with any of the product that has been carried over into the receiving flask, is transferred to a separatory funnel, separated from the aqueous hydrobromic acid formed during the reaction, and shaken with one-third its volume of concentrated sulfuric acid (Note 6). The lower acid layer is drawn off and discarded (Note 7). The residual bromide is mixed with an equal volume of 50 per cent methyl alcohol (Note 8), and aqueous ammonia is added with intermittent shaking until the solution is alkaline to phenolphthalein. The lower bromide layer is drawn off and washed once with an equal volume of 50 per cent methyl alcohol. It is then dried with calcium chloride, filtered, and distilled. The yield of product boiling at 199.5–201.5°/100 mm. or 134–135°/6 mm. is 220 g. (88 per cent of the theoretical amount) (Note 9).
2. Notes
1.
In order to obtain more efficient absorption of the
hydrogen bromide, a small bulb is blown on the end of the inlet tube, and a number of pin holes are made in it by means of a small, white-hot tungsten wire.
2.
The
dodecyl alcohol used was obtained by the fractionation of "Lorol"; its boiling point was
192.5–193.5°/100 mm. or
151–152°/21 mm. If the alcohol is not of good quality, the yield is somewhat lower.
Dodecyl alcohol may also be prepared according to the procedure given on
p. 372.
3.
The
hydrogen bromide is conveniently prepared by the direct combination of
hydrogen and bromine (p. 338). An excess of
hydrogen is to be avoided since it causes loss of product by volatilization.
4.
The heat of the reaction maintains the alcohol at this temperature until the preparation is nearly completed.
5.
For each mole of alcohol about
1.5 moles of hydrogen bromide is required, of which 1 mole is used to convert the alcohol to the bromide and approximately 0.5 mole to saturate the water formed in the reaction. The rate of addition should be regulated so as to require not less than an hour and a half. The Erlenmeyer flask that serves as a receiver should be weighed with the water in it before it is put in place. When the reaction is complete, the receiver gains weight rapidly and becomes warm owing to the heat of solution of the
hydrogen bromide in the water.
6.
The crude bromide must be shaken well with the
sulfuric acid. The function of the
sulfuric acid appears to be to convert any free alcohol to the acid sulfates, which is then soluble in
50 per cent methyl alcohol and ammonia.
7.
Care must be taken that the separation of the two layers in this and subsequent washings is complete. Failure to observe this precaution is usually the cause of a low yield.
8.
The use of
methyl alcohol prevents, to a large extent, the formation of troublesome emulsions. Less than
0.1 g. of dodecyl bromide dissolves in
100 cc. of 50 per cent methyl alcohol at room temperature.
9.
The authors have prepared other bromides by this method with the yields indicated below:
|
|
Bromide
|
Yield, %
|
Solubility of Bromides in Methyl Alcohol
|
|
|
Cyclohexyl
|
72–75
|
Less than 1 g. in 100 cc. of 65% methyl alcohol
|
|
n-Heptyl
|
87–90
|
Less than 0.5 g. in 100 cc. of 50% methyl alcohol
|
|
Tetradecyl
|
88–89
|
Less than 0.1 g. in 100 cc. of 50% methyl alcohol
|
|
Octadecyl
|
90–91
|
Practically insoluble in 90% methyl alcohol
|
|
Obviously for the lower bromides it is desirable to use no more methyl alcohol than is necessary to prevent the formation of an emulsion. A convenient method is to place the water, phenolphthalein, and crude bromide in a separatory funnel, and add ammonia until the mixture becomes pink. Methyl alcohol is then added in small portions until the emulsion is broken and two layers separate with a distinct boundary after the mixture has been agitated.
3. Discussion
The above method for preparing
n-dodecyl (lauryl) bromide is an adaptation of that of Ruzicka
1 and has been published.
2 It is thought to present some advantages in ease of manipulation and quality of product over the older method involving the action of aqueous
hydrobromic acid on the alcohol in the presence of
sulfuric acid.
3This preparation is referenced from:
Appendix
Chemical Abstracts Nomenclature (Collective Index Number);
(Registry Number)
calcium chloride (10043-52-4)
sulfuric acid (7664-93-9)
ammonia (7664-41-7)
methyl alcohol (67-56-1)
hydrogen (1333-74-0)
HYDROBROMIC ACID,
hydrogen bromide (10035-10-6)
bromine (7726-95-6)
Dodecane, 1-bromo-,
Dodecyl bromide,
n-DODECYL BROMIDE (143-15-7)
dodecyl alcohol,
n-dodecyl alcohol (112-53-8)
Cyclohexyl bromide (108-85-0)
phenolphthalein (77-09-8)
n-heptyl bromide (629-04-9)
Tetradecyl bromide (112-71-0)
Octadecyl bromide (112-89-0)
Copyright © 1921-, Organic Syntheses, Inc. All Rights Reserved