Phthalaldehyde-Sulfuric Acid

For the detection of the ergot alkaloids 0.2 g o-phthalaldehyde in 100 ml cone, sulfuric acid ( ) [15] or buffer solution is employed as spray solution. Cysteine [11, 12, 15, 19] or sulfurous acid [17] is occasionally substituted for mercapto-ethanol. 

Dipping solution Dissolve 0.5-1 g o-phthalaldehyde (phthaldialdehyde, OPA) in 45 ml methanol and cautiously add 5 ml sulfuric acid (95-97%) [31. 

Phthalaldehyde has been made by the action of potassium hydroxide on o- (dichloromethyl)benzaldehyde,6 by the hydrolysis of a,a,a, a -tetrachlorO -xylene,6 and by the hydrolysis of the a cqe/ja -tetraacetate of o-phthalaldehyde.3 The present method is essentially that of Thiele and Gunther.7-8 Hydrolysis of the tetrabromide may also be carried out by treatment with fuming sulfuric acid followed by water.9 For small-scale preparations of o-phthalaldehyde the reduction of N,N,N, N -tetra-methylphthalamide with lithium aluminum hydride is the method of preference.10... 

The benzo[c]furan (126) is probably formed on treatment of the tetra-Ione derivative 125 with o-phthalaldehyde in the presence of acetic anhydride/ sulfuric acid. ... 

It has been suggested that the benzo[c]furan (245) is formed from the tetralone derivative (244) on treatment with o-phthalaldehyde in acetic acid-sulfuric acid (71JCS(C)2175). 

Note o-Phthaldehyde in the presence of mercaptoethanol or cysteine has already been discussed as a reagent [4]. The present monograph describes the use of o-phthal-aldehyde in the presence of sulfuric acid. There are, in addition, a number of applications, which have been described, employing o-phthalaldehyde without any additives e. g. for the detection of primary arylamines, histamine, histidine and histidylpeptides (5-71. 

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