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Methaqualone (Quaalude) Synthesis

Synthesis of Methaqualone

From anthranilic acid (Toilet)2

This is an improved version of Klosa's original synthesis of methaqualone. The method first devised by him used phosphorous pentachloride instead of polyphosphoric acid as condensing agent, which during the reaction produced clouds of corrosive HCl gas1,9.

7g Anthranilic Acid, 5ml o-Toluidine and 4 ml glacial acetic acid was mixed in a round-bottomed flask. To this mixture was slowly added 40-50 grams of polyphosphoric acid, and the mixture was heated during 20-30 minutes to 140-160 C. After this, the mixture was heated to 180 C for 10 minutes, then cooled and poured in 150-200ml water, and neutralized with 20% Na2CO3 solution. Methanol was added until a lasting turbidity became present in the solution, and after one hour, the free base Methaqualone precipitated, mp 111-113 C, and was once more recrystallized in this fashion, mp 113-115 C. Yield 55%.

From anthranilic acid5,6

This method is similar to the one used by Klosa, but this one drives out the water byproduct from the reaction mixture with heat, instead of letting polyphosphoric acid bind it. This method also manages to push the yield a little further. The product formed in the first step is N-acetylanthranilic acid, which can be made as described in the precursors section below. If so, begin with the addition of o-Toluidine to the already made N-acetylanthranilic acid.

Anthranilic acid (10 grams) is dissolved in acetic anhydride (20 ml) and the temperature raised progressively to 190-200 C at which temperature distillation takes place. The last traces of acetic acid are removed under vacuum and after cooling to about 50-60 C, o-toluidine (10 grams) is added in portions. The temperature is then raised to 170-200 ° C when the excess water and o-toluidine is gradually distilled off, finally maintaining the temperature at 180-200 ° C for 2 hours. After cooling to about 100 C, 30ml dilute HCl is added and the mixture boiled and stirred. The solution is neutralized with NaOH with stirring, and the crude product which separates is recrystallized twice from alcohol. The yield is 70% of theory.

From N-acetylanthranilic acid5

This method is similar to Klosa's first synthesis of methaqualone, the difference being that this one uses POCl3 instead of PCl5, and uses ready made N-acetylanthranilic acid. By performing the reaction in toluene, the yield is very good. In spite of this, the method is best left alone, as the POCl3 will release lots of HCl gas during decomposition.

o-Toluidine (10 grams) is mixed with a solution of N-acetylanthranilic acid (20 grams) in toluene (30 grams) in a vessel equipped with a stirrer and means of cooling. A solution of phosphorus oxychloride (10 grams) in toluene (30 grams) is added dropwise with stirring and then the temperature is raised to the boiling point for two hours with further stirring. After cooling, the precipitate so formed is filtered off, dried and dissolved in boiling dilute HCl. On cooling and making alkaline with NaOH, a viscous oil separates which crystallises after a few hours. The crystals are collected the next day and purified by recrystallization from alcohol to yield about 80% of the theoretical quantity of methaqualone freebase (mp 114-115 C). The salts my be obtained by the addition of the appropriate acids to the base formed above.

From Isatoic Anhydrides (Manhas)3

Method A

A mixture of isatoic anhydride (1.6 g, 0.01 mole) and o-toluidine (1.1 g, 0.01 mol) is heated to 120 for 2 hours. The reaction mixture after cooling is triturated with ether (or dissolve the brown mixture in warm acetone and add water to crash out the crystals). The resulting solid is collected by suction and recrystallized from a 50:50 mixture of dichloromethane and petroleum ether to give the intermediate aminoamide (2,2'-dimethylbenzanilide): yield: 1.7 g (75%): m.p. 110 .

A mixture of 2,2'-dimethylbenzanilide (0.5 g, 0.0025 mole), acetylacetone (0.39g, 0.0025 mol) in ethanol (30 ml) containing a few drops of concentrated hydrochloric acid is refluxed for 1 h. On cooling the title compound separated as the hydrochloride salt: yield: 0.59 g, (85%), m.p. 235-237 .

  1. Isatoic anhydride condenses with o-Toluidine to give 2,2'-dimethylbenzanilide
  2. 2,2'-Dimethylbenzanilide condenses with acetylacetone to form Methaqualone
Method B

A mixture of 8g isatoic anhydride and 5.5g o-toluidine in toluene (500-750 ml) is refluxed for two hours. Acetylacetone (2.5g) containing a few ml of concentrated hydrochloric acid (to form the hydrochloride) is then added, and refluxing is continued for another hour. Evaporation of the solvent gives methaqualone hydrochloride, which is purified by recrystallization from hot methanol. The yield is 80%.