122
INDUSTRIAL AND ENGINEERING CHEMISTRY
total number of oxygen equivalents demanded is 14. The total reaction is shown as follows: C6Hs07 14Ce(ClO&-5H20 = 4C02 SHCOOH 84C10a- 14Hf 14Cefft
+
++
+
+
+
The formulas for the group oxidation of various type reactions are given in the following summary: XI. Polyhydric Alcohols CH20H.(CHOH),.CH20H - (2n
6)e- + ( n + 2)H20 7 ++2)HCOOH + 12n + 6)H XII. Polyhydric Alcohol Monocarbdxylic Acids CH*OH.(CHOH),COOH - (2n + 4)e- + ( n + l\HQO = -(n + lyHCOOHi+ (in'+ 4)Hi.-j-C02 XIII. Polyhydric Dicarbc3xylic Acids COOH.(CHOH),. COOH - (2n + 4)e- + nHpO = :nHCOOH + - t . (2n + 4)" XIV. Aldoses CH2OH.(CHOH),.CHO - (2n + 4)e- + ( n + 2)H20 =, (n+ 2)HCOOH + (2n + 4)H (n
~
_--
nrln
I
L ~ W Z
~
XV. Ketoses - (2n 8)e- (n 3)H20 = CH~OH.(CHOH),.CO.CHZOH (TL 2)HCOOH (2n S)HT COz
+
+ + ++ + +
Conditions Governing Experimental Reaction Procedures For the quantitative and stoichiometric oxidation of organic compounds several requirements must be fulfilled. Each organic molecule must react to give definite end products and all side reactions must be excluded. The end products must not be further oxidized under the defined experimental conditions. A time limit for reaction has been established of 120 minutes or less. Any reaction for which an odd number or fractional number of equivalents are employed is known to be empirical and unsatisfactory. Solutions of perchlorato-ceric acid in 4 N perchloric acid may be heated a t 60" C. for 60 minutes without appreciable loss in titer due to the oxidation of water (reaction V). Formic acid is not appreciably oxidized by the same cerate solution, a t the same temperature, in the same period of time. Amounts of acetic acid experimentally encountered may be present without appreciable error during periods of 60 minutes a t 50" C. With acetaldehyde and acetone present as products of the reaction of oxidation, more than 5 minutes a t 10" C. introduces appreciable error. These values were established by a procedure duplicating that described by the present authors (6) for the case of the determination of glycerol. Testing the general procedure applicable in specific instances consisted in the addition of known amounts of the various organic compoundst o 4 N perchloric acid solutions containing about a twofold excess of perchlorato-cerate ion. The reaction was allowed to develop at a definite temperature for specified periods of time and at the end the reacting solution was diluted by the use of an equal volume of water. A drop of 0.025 M nitro-ferroin indicator was added and the excess perchlorato-cerate ion was titrated, using standard sodium pxalate solution, until the fist drop of excess produced a faint pink solution. The reduction of excess oxidant was carried out at ordinary temperatures. The end products were either qualitatively detected or predicted by analogy, and the experimental conditions were limited to those permissible in the presence of the known end products. If the oxygen equivalent calculated did not agree with that experimentally found, side reactions were indicated demanding altered conditions or elimination of the procedure from practical application. The results of the analyses of a series of pure organic compounds are given in Table I.
Summary The mechanism of quantitative oxidation of organic compounds using periodic acid as oxidant has been described. The same mechanism has been applied to the oxidation of organic compounds using the perchlorate-cerate ion, Ce(ClO,)S--, in the presence of 4 M perchloric acid. The latter procedure has been studied for a considerable number of
Vol. 15, No. 2
individual cases and the type reactions involved make possible its application to a more extensive series of compounds. The use of the perchlorato-cerate ion and periodate ion in these procedures follows the same general scheme. The organic compound is oxidized by excess of oxidant in acid solution for a specified time a t a given temperature, after which the excess oxidant is evaluated using a standard reducing agent. The use of periodic acid is more complicated than that of the perchlorato-cerate ion because the excess periodate ion must be determined in the presence of the iodate ion, necessitating the use of an added standard solution. The perchlorato-cerate ion is more extensive in its applicability, the number of oxidation equivalents required is larger, and the speed of the reactions in general greater than in the case of the periodate ion. All reactions by both procedures are stoichiometric rather than empirical, and an exceptional degree of accuracy is obtainable in all cases. The methods apply to aliphatic compounds and are not specific in their action but require special treatment to isolate the substance to be determined if interfering substances are present.
Literature Cited (1) Fleury and Fatome, J. pharm.chim.,21,247 (1935). (2) Malamade. Bull. SOC. chim..43. 683 (1928). (3) Smitc, "Cerate Oxidimetry", ' Columbus; Ohio, G. Frederick Smith Chemical Co., 1942. (4) Smith and Duke, IND.ENG.CHEM., ANAL.ED.,13,658(1941). (5) Stamm, 2.anal. Chem.,47,191 (1934);48,150,710(1935). THEwork reported in this paper was carried out under the grant of the G. Frederick Smith Chemical Company fellowship in analytical chemistry.
Thimble Supports for Faster Soxhlet Extraction WALTER C. TOBIE, 22 Lockwood Ave., Old Greenwich, Conn.
T
HE insertion of a piece of glass rod a t an angle into the extractor (midpiece) of a Soxhlet apparatus to raise the thimble off the bottom, thus securing better drainage and a more rapid rate of extraction, has recently been recommended (1). The author has occasionally used this and similar methods in the past, particularly where it was necessary to use a thimble shorter than the height of the siphon, so that undissolved matter might have been displaced from the thimble mechanically if the liquid had been allowed to rise above the top of the thimble. However, an oblique glass rod was not always satisfactory as a thimble support. When inserting or removing the thimble, there was sometimes a tendency for the rod to shift into such a position that its lower end obstructed the outlet of the siphon, thus impeding or preventing proper extraction. If this trouble is encountered, a ground-glass stopper with a flat or mushroom-type top may be inverted in the bottom of the extractor to support the thimble without obstructing the siphon, To avoid breakage, it should be carefully inserted or removed with crucible tongs or forceps. By somewhat diminishing the volume of liquid which can collect a t each filling, the glass stopper promotes more frequent siphoning and faster extraction. A weighing bottle, or large homeopathic vial, of appropriate height and diameter, inverted in the extractor, also serves as an effective thimble support in some cases.
Literature Cited (1) Neustadt, M.
H.,IND.ENQ.CHEM.,ANALED.,14,431 (1942).
