Such a series of typical compounds are the benzene dicarboxylic acids (phthalic acids), C 6 H 4 (000H) 2.
We may here mention the synthesis of oxyuvitic ester (5-methyl-4-oxy-I-3-benzene dicarboxylic ester) by the condensation of two molecules of sodium acetoacetic ester with one of chloroform (Ann., 1883, 222, p. 249).
Thus ortho-phenylene diamine yields the following products: N H N ./`N; Xn NZ In some cases oxidation of condensed benzenoid-heterocyclic nuclei results in the rupture of the heterocyclic ring with the formation of a benzene dicarboxylic acid; but if the aromatic nucleus be weakened by the introduction of an amino group, then it is the benzenoid nucleus which is destroyed and a dicarboxylic acid of the heterocyclic ring system obtained.
As a useful preliminary it is convenient to divide heterocyclic ring systems into two leading groups: (I) systems resulting from simple internal dehydration (or similar condensations) of saturated aliphatic compounds - such compounds are: the internal anhydrides or cyclic ethers of the glycols and thioglycols (ethylene oxide, &c.); the cyclic alkyleneimides resulting from the splitting off of ammonia between the amino groups of diaminoparaffins (pyrrolidine, piperazine, &c.); the cyclic esters of oxycarboxylic acids (lactones, lactides); the internal anhydrides of aminocarboxylic acids (lactams, betaines); cyclic derivatives of dicarboxylic acids (anhydrides, imides, alkylen-esters, alkylenamides, &c.).
Reduction of this ester leads to the formation of ammonia, hydroxylamine, and dimethyl pyrrol dicarboxylic ester, C(CH3): C C02R HN< C(CO 2 R) :C CH3.
On oxidation with potassium permanganate it yields acridinic acid (quinoline -a-(-dicarboxylic acid) C 9 H 5 N(COOH) 2.
The plane projection of molecular structures which differ stereochemically is discussed under Stereoisomerism; in this place it suffices to say that, since the terminal groups of the hexaldose molecule are different and four asymmetric carbon atoms are present, sixteen hexaldoses are possible; and for the hexahydric alcohols which they yield on reduction, and the tetrahydric dicarboxylic acids which they give on oxidation, only ten forms are possible.
It melts at 55° C. and boils at 115° C. It may also be obtained by elimination of carbon dioxide from the pyrazine dicarboxylic acid formed when quinoxaline is oxidized with alkaline potassium permanganate (S.
21-27, and 31), and are diphenyl tetramethylene dicarboxylic acids.
Thus for dicarboxylic acids (CO 2 H = X) the possibilities are represented by X X (cis), X x (trans), .X X (I).
Cyclo-propane carboxylic acid, C 3 H 5 CO 2 H, is prepared by heating the 1.1- dicarboxylic acid; and by the hydrolysis of its nitrile, formed by heating y-chlorbutyro-nitrile with potash (L.
The '1.1' dicarboxylic acid is prepared from ethylene dibromide and sodio-malonic ester.
The cis 1.2-cyclo-propane dicarboxylic acid is formed by eliminating carbon dioxide from cyclo-propane tricarboxylic acid -1.2.3 (from 43-dibrompropionic ester and sodio-malonic ester).
The trans-acid is produced on heating pyrazolin-4.5-dicarboxylic ester, or by the action of alcoholic potash on a-bromglutaric ester.
When sodio-malonic ester is condensed with trimethylene bromide the chief product is ethyl pentane tetracarboxylate, tetramethylene dicarboxylic ester being also formed, and from this the free acid may be obtained on hydrolysis.
The a-acid is diphenyl-2.4-cyclo-butane dicarboxylic acid -1.3; and the /3-acid diphenyl-3.4-cyclo-butane dicarboxylic acid -1.2.
It may be prepared synthetically by fusing its dicarboxylic ester (from malonic ester and sodio malonic ester at 145° C.) with potash (C. W.
An important derivative is succino-succinic acid, C 6 H 6 0 2 (CO 2 H) 21 or cyclo-hexanedione-2.5-dicarboxylic acid-I.
Tetrahydrophthalic acids (cyclo - hexene dicarboxylic acids), C 6 H 8 (CO 2 H) 2.
On oxidation it yields methyl granatic ester, which, by the exhaustive methylation process, is converted into homopiperylene dicarboxylic ester, HO 2 C CH :CH CH 2 CH 2 CH :C. H CO 2 H, from which suberic acid may be obtained on reduction.
PHTHALIC ACIDS, or Benzene Dicarboxylic Acids, CmH 4 (CO 2 H) 2.
It may be synthesized from toluene; more interesting is its production when acetone dicarboxylic ester is condensed with the aid of sodium.