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                    Preparation of DL-Amphetamine Phosphate
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1 mol of phenyl-2-nitropropene, C6H5CH=C(CH3)NO2, is dissolved with a solvent 
prepared by mixing 1000ml of ethanol with 500ml of acetic acid and 500ml of 12 N 
sulfuric acid. The resultant solution is placed in the cathode compartment of a 
divided electrolytic cell containing a metallic cathode of mercury, copper, or 
other metal of similar nature. Current is passed, using a current density of 
~0.2 amp/cm2 of cathode surface. The temperature is kept at about 40°C during 
the electrolysis which is continued until at least eight Faradays of electricity 
have been passed.

When the reduction is completed, the amphetamine may be separated from the 
solution. A convenient way of doing this is by removing the ethanol and ethyl 
acetate present by evaporation and then making the residual solution strongly 
alkaline by addition of caustic alkali. The basic layer thus formed is separated 
from the aqueous solution and contains the desired amphetamine freebase.

135 g (1 mol) of amphetamine freebase were stirred into 300ml of acetone in a 
1000ml erlenmeyer flask. To the resultant solution there were slowly added under 
constant agitation 115.3 g of 85% phosphoric acid (containing 1 mol of H3PO4), 
care being taken to avoid any sudden rise in temperature or local overheating 
due to the considerable amount of heat that is evolved. During the addition of 
the phosphoric acid a fine, white, flocculent precipitate appears which becomes 
more and more dense and abundant, as the quantity of added acid increases.

When the entire quantity of the phosphoric acid has thus been added, agitation 
of the mixture is continued for about a half-hour or more to insure complete 
conversion. The precipitate is then allowed to settle, the supernatant liquid 
is drawn off, and the residue is filtered. The precipitate thus separated is 
washed with acetone and is then dried by evaporation to constant weight. 
It forms a fine, white, impalpable powder consisting of pure monobasic 
amphetamine phosphate.

Ref: Pharmaceutical Manufaturing encyclopedia (1988)

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