? ASTIQl-I'rY i the st:ene was laid for one of tlie inodcrn romances of chemistry. In 1421 the Chinese, visiting the beaiitiful island of Formosa (Q), found among the numcri)us articles that attracted them a su1,stance wit.11 wliicb tlie natirrs were familiar and vhicli hiid a ires11 and pleasant odor. In the interior of that country of mountains thcre arc wonderful stret,ches of virgin forest wit11 gigantic tree fwm. I n these virgin forests grow stately cainplm trees, filling the air with their I,shny scent that can be smelled Sm miles around. Man the ruorld over is attracted by ircaiitiful crystals, plewsant odors, and gleitniing white prodiicts. l t was a delight to tlie aborigincs of I'orirrosa to produce such a siilistance II? chopping these magnificent trees into t.liin pieces, putting them through a simple distillat.ion pro rating t,he camphor from the oil. Tlien a refineiiient was accomplisiied by taking advantage of one of t.lie Iiiiysical properties to sublime the pure material from the criidc and to produce the pure crystalline product that eoirld be pressed into sniall cakes and serve as symliols of pagan belief and amulets to insure health. The Chinese prized it liighly, and traders from tlie r e a r East and Europe procured it and carried it home as evidence of the attractiveness of the Orient,. It vas first used in India and then in Egypt. It was emphiyed in Turkey by tlie end of the fourteenth century for medicinal purposes, and siniila.rly by tlie Arabs as oarly as the eleventh century.
I
iI19
rZlttiougli visited by the Dutch and Spaniitrds, Formosa reinaiired in the hands of the Chinese until 1895, when, as the result of the Sino-Japanese war, it mas ceded to Japan. Since tlicn, owing to the unremitting and intelligent efforts of the .Japanese, I'ornrosa has prospered as never before and has now gained for itself a world market in many comrriodities, principal among which are tea and camlilior. In 1'333 the value of camplior and it,s by-products aniounted to 10,000,000 yen. ItMINATION OF (:AMPHOIl
kkl%UCTUItE
During the nineteenth century the structure of carnplior occnsirmed moch curiosity on t.he part of chemists. Modern nian Iias never been content to be restricted hy nature and the obvious desiralile properties of camphor gave the inceritive to scientists to work out the secret of its structure and to build it up from more available substances by synt,hetic p J C esses. Ihimas in 1832 established the molecular formula as being ('dT,&. It was early noted (3) that, by dehydration with phosphorous pentoxide, camphor was converted into pcynene, while by treatment with iodine, carvacrol (2liydroxy-p-cymene) was formed. These results clearly pointed to a benzene skeleton. Rosengarten in 1785 oxidized camphor with nitric acid and obtained camphoric acid, a compound which has played an important part in the final determination of the structure of
INDUSTRIAL
590
AND ENGINEERING CHEMISTRY
camphor. Various derivatives and reaction products followed. In 1838 Martius announced the existence of borneol, and in 1843 Gerhardt made camphor by oxidation of borneol. Weyl in 1868 showed camphor to be a ketone, as evidenced from the formation of derivatives such as an oxime, a bromophenylhydrazone, and a semi-carbazone. In 1871 Krachler found a second acid, camphoronic, among the oxidation products, and it was the elucidation of the structure of this acid by Bredt in 1893 which led ultimately to the correct interpretation of the structure of camphor. Camphor structures, as thought to be in 1690 and as known to be in 1893, follow:
Vol. 26, No. 6
the other depends on economic considerations, such as original cost and credit obtained for by-products. Greek turpentine contains 95 per cent total pinene. The French product is next highest, and, as indicated, the American contains 92 per cent.
METHODSOF SYNTHESIS Two laboratory methods of synthesis of camphor have been employed (6). One starts with pinene and goes to bornyl chloride and camphene, and the latter is directly oxidized to camphor:
H H-t-H
H
H ALPHA-PINENE
BORNYL CHLORIDE
W
CY
H ALCHEM15TIC FORMULA-1690
BRCDT FORMULA-1893
The year 1893 was in the midst of one of the most remarkable CAPlPHENE CAPIPHOR periods of chemical developments the world has known. German chemists, as well as some others, undertook the problem of duplicating camphor. Curiously enough, although the The other is the same through the camphene step but then practical goal has been attained, the natural product has converts the camphene to borneol or isoborneol and oxidizes never been exactly duplicated since it has the physical these to camphor: property of optical rotation whereas the synthetic product is practically inactive. This difference detracts not a t all from c H3 H the synthetic product since it can be used for all purposes, including medical, with equally good results, as indicated by the fact that it is included in the German and the British Pharmacopeias. The cue to the successful synthesis of camphor was given by PINENE BORNYL CHLORIDE CAMPHENE the fact that it was possible to obtain some camphor from borneol and it was also known that borneol, as well as similar substances, could be derived from turpentine. The constituent of turpentine of real importance was pinene (4). The pinenes are the main constituents of the various turpentine oils which are obtained by steam distillation of pine 150-BORNEOL ACETATE 150-BORNEOL CAMPHOR stumps or the resinous exudations of various coniferous trees. a-Pinene is by far the most widely distributed of all the natural terpenes; in addition, turpentine contains an isoSimple though these syntheses appear, it was one thing to meric beta form, nopinene, which occurs in much smaller prepare small quantities of camphor in the laboratory and quantities; quite another to manufacture it economicallv. Early in the twentieth century the Germans had reached the point of manufacturing a t a price which could then compete with the natural product, as had several smaller concerns in France, Switzerland, and Italy. These commercial processes involved the second procedure just mentioned and the now commonly accepted general practice of starting with turpentine, fractionating to obtain pure pinene, saturating with -A L PHA-P INE N E BETA-PINENE hydrogen chloride to form bornyl chloride, hydrolyzing to form camphene, esterifying, saponifying to form isoborneol, The pinene contents of gum and wood turpentine, respec- and oxidizing to camphor. tively, are as follows:
TABLEI.
IMPORTATIONS OF CAMPHOR TO THE UWITED
G U MTURPENTINE Woon TURPENTINE &-Pinene &.Pinene
High-boiling terpenes Dipentene
%
%
74 18 8
77
..
..8
15
Both a- and /3-pinene are useful in the manufacture of camphor, and it is evident, therefore, that the effective portion of gum turpentine is 92 per cent whereas only 77 per cent of the wood turpentine is of direct value. The use of one or
STATES(2) (In pounds) NATURAL
SYNTEE~C
YEAR 2,944,478 1926 2,933,784 1927 2,264,916 1928 3,957,282 1929 2,393,691 1930 1,828,091 1931 1,459,674 1932 267,508 1933" a Up t o and including July,
CRUDE
2 018 971 1:689:714 4,364,661 4,203,795 1,058,393 1,963,796 1,799,201 996,694 1933.
u. s. P.
NATURAL REFINED
1,169,779 1,480,851 1,176,047 1,031,584 1,431,438 1,161,876 1,034,059 945,201
TOTAL
6,138,228 6,104,349 7,805,624 9,592,515 4,483,668 4,953,763 4.292,934 2,209,403
Junc, 1934
I 3 11 U S T R I A I.
A N II E X G I N E E K I N G
C H E M I S T I< Y
591
Dumning the dough
Dough mixer
PYROXYLIN MIX~NC OPERATION Utilizing this general method, tlie Europeans improved their working conditions and were able gradually to replace a iiortion oi the natural product until in 1931 it is estimated they produced 12,000,000 pounds. Substantial quantities were exported to the United States as shown by Table I. During the 7-year period, 1926 to 1932, inclusive, the total mmphor imports averaged about 5,000,000 pounds annually. CO\lMEi
