INDUSTRIAL AND ENGINEERING CHEMISTRY
50
Since, however, Petrie7 has more recently described a coloring matter present in Acacia flowers, stated also by Klein to contain an anthochlor, which proved to be a rhamnoside of the flavonol, kaempferol, it is evident that lime-rind phlobatannin is not identical with Klein's pigment.
On pouring the mixture into water, a dense greenish black precipitate separated, having the properties of a ghlobaphene. Nessler's solution gave a yellow precipitate, which quickly turned brown and finally olive green on standing. Sodium nitrite, in the presence of dilute hydrochloric acid, gave an evanescent red-brown coloration. Uranium acetate gave a cherry red coloration; stannous chloride, a bright yellow precipitate; neutral lead acetate fi buff precipitate, soluble in acetic acid; and basic lead acetate, a bright yellow lake. Acetylation of the solid phlobatannin yielded a brownish black amorphous powder, which could not be obtained in crystalline form. Heating at 200" C. in glycerol for half an hour yielded no definite fission products. The behavior of the substance towards caustic potash under different conditions was therefore examined. Fusion with potash a t temperatures not exceeding 240" C., and subsequent extraction of the neutralized melt with ether, yielded a small amount of crystalline matter, which proved to be mainly protocatechuic acid. Hydrolysis with aqueous or alcoholic solutions of potash a t boiling temperature yielded ether extracts having a bright yellow color. On evaporation these left tarry residues, insoluble in cold water, moderately soluble in hot water, but easily soluble in alcohol. The largest proportional yield of ether-soluble matter was obtained when aqueous potash of 20 per cent concentration was employed. In no case, however, was the proportionate amount of residue very large, so that its exact identity could not be completely established. The stability of lime-rind phlobatannin towards caustic potash appears to be a highly characteristic property of the substance. After purification by treatment with charcoal and with suitable solvents, the small amount of crystalline matter that remained showed a melting point of approximately 216" C. Its aqueous solution gave a pure green coloration with ferric chloride, turning blue, violet, and red on addition of dilute sodium bicarbonate. It was therefore concluded that one of the products of alkaline hydrolysis of lime-rind phlobatannin is caffeic acid. It is noteworthy that lime leaves contain a yellow coloring matter identical with that isolated from the fruit rind. The reactions of lime-rind phlobatannin, and its behavior towards potash, suggest that it is closely related to caffetannic acid. Note-Caffetannic acid of coffee was first described by Rochleder.8 It was subsequently found to be widely distributed in nature. Kuntt-Krauseg proved that caff etannic acid yields caffeic acid on alkaline hydrolysis. Gorter'o later showed that the tannin is a mixture of two acids, chlorogenic and coffalic, of which the first yields caffeic acid and quinic acid on hydrolysis." Freudenberglz suggested that chlorogenic acid is a depside. The recent work of Oparin13 indicates that chlorogenic acid may be the chromogen of a respiratory pigment of the type described by Palladin.14 On the other hand, chlorogenic acid, by virtue of its o-dihydroxy constituent, caffeic acid, may function as one of the three factors which, according to Onslow16 comprise a plant oxidase system. Proc. Linnean Soc., N . S . Wales, 48, 356 (1923); C. A . , 18, 685 (1924). 8 Ann., 69, 300 (1847). 0 Arch. Pharm., 281,613 (1893); J . Chem. SOG.(London), 66,327A (1894). 10 Ann., 868, 327 (1908); J . Chem SOL.(London), 94, 186A (1908). 11 Ann., 869, 217 (1908); J. Chem. Soc. (London), 94, 345A (1908). I* Ber., 6SB, 232 (1920); J . Chem SOC.(London), 118,3228 (1920). 18 Biochem. Z . , 124, 90 (1921). P. Blakiston's Son & Co. 14 "Plant Physiology," 1918, p. 202. Bzochem. J . , 14, 535 (1920). 7
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Comparison with this substance, extracted for the purpose from fresh coffee berries, showed, however, that the two substances are not identical. For example, the color of solutions of caffetannic acid and of the phlobaphene derived therefrom is deep red instead of brown. Furthermore, caffetannic acid gives a deep green coloration with ferric chloride, whereas the color given with lime-rind phlobatannin is brownish green. It also yields a green compound with ammonium hydroxide (viridic acid), whereas lime-rind phlobatannin gives no such product. Practical Applications
Fresh lime juice intended for consumption as an article of food should be bottled and stored with complete exclusion of air, otherwise oxidation leads to the development of a dark color, and possibly also to some loss in antiscorbutic activity. Zilva,16has recently shown that oxidation, especially in the presence of alkali, destroys the antiscorbutic fraction of lemon juice. A preliminary heating to expel gases, and partly to pasteurize the juice, also aids in preventing darkening. If excessive, however, it may produce an undesirable flavor. Carbon dioxide or hydrogen may be used to replace air in storage vessels, or the vessels may be evacuated before ~ea1ing.l~ The coloring matter of lime juice intended for the manufacture of citric acid may be partially removed by longcontinued boiling in contact with air. This leads to the formation of insoluble phlobaphene, which may subsequently be removed by filtration. Partly for this reason, overseas manufacturers do not object to concentrated lime juice prepared by rapid evaporation in open vessels as a raw material for the manufacture of citric acid. There would thus appear to bc no advantage in the use of vacuum evaporators for concentrating lime juice, beyond the loss in citric acid sustained by the grower who exports that product. During the preparation of calcium citrate from lime juice, as an intermediate stage in the manufacture of citric acid,1* excessive liming should be strictly avoided. The autoxidation of polyhydroxy phenols probably does not become appreciable until the reaction of the solution is more alkaline than pH 7.3 to 7.8, but it is highly sensitive to further in- ' creases of alkalinity above this range. La Mer and Rideall9 have demonstrated these facts for the autoxidation of hydroquinone. At very high alkalinity the coloring matter of lime juice appears to be precipitated, but a relatively large amount of solid calcium hydroxide is required to produce this final result. Thorough washing with water, especially hot water, is very effective in removing the unoxidized coloring matter present in commercial calcium citrate prepared by careful liming. It is almost ine€fective if applied to calcium citrate that contains the tarry products of oxidation of the phlobatannin. To procure a high-grade product, the citrate should therefore be washed immediately after precipitation. Biochem. J . , 18, 182 (1924). McDermott, THIS JOURNAL, 8, 136 (1916); and University of Florida, Agr. Expt. Sta , Bull. 136 (1917). 1s Wilson, THIS JOURNAL, 13, 554 (1921), gives a full account of the manufacture of citric acid from lemons. 18 J . A m , Chem. Soc., 46, 228 (1924). 18 17
November Chemical Engineering Education in England-On 12, the Ramsay Memorial Laboratory of Chemical Engineering was opened at University College in London. Although chemical engineering has been taught a t other British institutions, the opening of this new laboratory marks the commencement of a definite department of chemical engineering in a British University. The syllabus of instruction drawn up by Professor Williams is very attractive, and it is noteworthy that the physical and physical chemical aspects of chemical engineering will be given the fullest possible treatment.
