A SEQUENCE OF SYNTHESIS IN THE GENERAL ORGANIC LABORATORY CLASS ERWIN F. LANGE and ROY TERANISHI Portland State Extension Center, Portland, Oregon BERT E. CHRISTENSEN Oregon State College, C o ~ d i S Oregon ,
slowly over a water bath, but by using an oil bath at B E G I N N I N G organic chemistry students can receive valuable synthetic experience by completing a sequence 120" to 130°C. the oxidation can be completed in five of preparations in which a compound that has been to six hours. Part of the terephthalic acid was treated with PCls. prepared is used as starting material for the next o p eration. Experience indicates that students do well The chlorination product in turn was slowly added to and are interested in such procedures if the chosen methanol, which was then diluted with water, yielding compounds are of practical importance and if the pro- crystals of dimethylterephthalate. This compound cedures can be accomplished without undue difficulties. is today of tremendous commercial importance in the The following sequence of reactions has been sue- manufacture of synthetic fibers. The remaining terephthalic was nitrated with conCH, COOH COOH centrated HN08 and fuming HzSO~. If the usual prep-
o""'0 / CH,
COOH
/
NO* COOH
1
SnCL HCI
""=
0
F' C=O
b
1
CHIOH
//
0
// \
//
8
C-0-CH3
PROCEDURES (1) Oxidation of p-Xylene. In a two-liter flask equipped with a stirrer and reflux condenser were placed 15 g. of p-xylene, 10 g. NaOH, 90 g. KMn04, and one 1. of water. This mixture was refluxed a t 120°C. until the color of KMnO4 was no longer visible. The oxidation mixture was filtered to remove the Mn02, washed, and the filtrate acidified with dilute H,S04. The crude terephthalic acid was filtered, washed, dried, and used for the next preparation; yield, 20 g. (85per cent). ( 2 ) Nitration of Terephthalic A&. Ten g. of crude terephthalic acid, 50 ml. of fuming H2S04, and 50 ml. of conc. HNO, were placed in a 250-ml. beaker. The mixture was heated until all of the acid went into solution and then allowed to cool. The cooled mixture was poured over cracked ice. The precipitate of nitroterephthalic was collected on a filter, washed with water, and dried. A sample recrystallized from water melts at 269-70°C. Yield, 9.3 g. (73 per cent). (3) Esterification of Terephthalic Acid. One g. of terephthalic acid was carefully heated in a test tube with one g. of PClr until the mixture was melted. The mixture was carefully poured into 15 ml. of methanol.
COOH
0
Ho~-@
I
o
students, aration ofthis nitrobenzene procedure has is ofalready value inbeen noting done theby differthe ences in nitration conditions owing to the deactivating effects of the two carboxyl groups. This step results in the lowest yield but most students reported 60 per cent or better. The nitroterephthalic acid is easily reduced to aminoterephthalic acid by refluxing with HC1 and stannous chloride. The aminoterephthalic acid is a convenient starting material for the preparation (via cyclization) of 4quinazolone-7-carhoxylic acid which offers the possibility of other interesting syntheses.
NH
I(,
-0-CRs
\o cessfully performed by beginning students. The series illustrates a number of procedures common t o aromatic chemistry: oxidation, esterification, nitration, reduction, and cyclization. The starting material was p-xylene (95 per cent, from Oronite Chemical Company) which was oxidized t o terephthalic acid. This oxidation is practically quantitative and is not much more difficult to accomplish than the usual preparation of benzoic acid. It was found that the oxidation proceeds 40
JANUARY, 1955
41
The methanol was diluted with water until the preoipi- was filtered, washed with cold water, and dried. The tate of dimethylterephthalate appeared. The ester aminoterephthalic acid is a lemon-yellow solid which was filtered, washed with water, and dried. Recrystal- melts with decomposition ahove 300°C. Yield, 5.9 g. lization from methanol produced beautiful white (89 per cent). needle-like crystals melting a t 140°C. ( 5 ) Preparation of 4-Quinmobne-7-Carboxylic Acid. ( 4 ) Reduction of Nitroterephthalic Aeid. To a hot When 5 g. of aminoterephthalic acid is heated with a solution of 30 g. of SnC1, in 100 ml. of cone. HC1 was slight excess of formamide, a gelatinous mass is obadded 8 g. of nitroterephthalic, and the mixture was tained from which the quinazolone carhoxylic acid is refluxed over a water bath for one hour. Upon cooling obtained by recrystallization from water. It melts the aminoterephthalic was precipitated. The acid with decomposition ahove 300°C.
