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TABLE I. MOLECULAR WEIGHTS DETERMINED BY METHOD DESCRIBED Substance a-Nitronaphthalene, CloHiNOs Rotenone, CznHziOa 2-(3-Chlorobensoyl)-benzoic acid, C14H90sCl o-Chlorobensoic acid, ClHsOzCl Pyrotenulin, CliHzaO4 Isotenulin, CliHnO6 Ferulic acid CIOHIOOI p,p'-Dibrododiphenyl, CnHaBrz
420-
0 0
821
ANALYTICAL EDITION
November 15, 1941
-
400-
w I
Molecular Weight Found Calculated 173.1 173.7 393.3 394.3
260.7 156.5 288.3
255 157.4 288.4
195.5 313
312
304
306.4 198.1
23.90-I
0
-
-
8
I
I 4
I
I 6
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1 8
1
1
1
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1 \e
1
1 I6
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,
,
IS
16
20
DAYS
FIGURE 3. AZOBENZENE-PYROTENULIN Solvent, chloroform: solutions 0.1367 molar a t equilibrium. weight of pyrotenulin, 288.3: found, 288.4
Molecular
The essential experimental factor in this determination is the maintenance of the apparatus in an isothermal condition. A very simple way to do this is to conduct the experiment at room temperature in a heavy metal container, such as an aluminum pressure cooker, which has a high thermal conductivity. Under these conditions the time necessary for a pair of solutions to reach equilibrium is greater than a t elevated temperatures, but the simplicity of the procedure and the accuracy of the results warrant its use. The duration of the
experiment is also dependent upon the concentration of the solutions, their relative molarity when prepared, and the solvent used. The best solvents are those with high vapor pressures. Ether, acetone, ethyl bromide, and chloroform have been employed, but others would undoubtedly be as good. These factors can be judged by a study of the curves in Figures 2 and 3, where ether and chloroform are the respective solvents. Aeobenzene is an excellent standard where organic solvents areused. It is easily purified, is permanent in the air, and is readily soluble in most solvents, and the color of its solution distinguishes it from the unknown. The procedure as outlined has given uniformly good results with all classes of compounds studied and appears to be generally applicable. It is thus one of the best methods available for the determination of molecular weights. Several results obtained by it are presented in Table I.
Literature Cited (1) Signer, R., Ann., 478, 246 (1930).
Determination of Hydroxyl Content of Organic Compounds Acetyl Chloride as a Reagent BERT E. CHRISTENSEN, LLOYD PENNIMGTON, AND P . KEENE DIMICK Oregon State College, Corvallis, Ore.
T
H E simplest methods for the determination of the hydroxyl radical in organic compounds are those based on esterification procedures. Acetic anhydride with and without pyridine has been widely used in this connection @ , 3,4) 6), but although acetyl chloride is a much more active acetylating agent, little attention has been given to the possibility of using it in quantitative work (6). It is difficult to measure and handle small amounts of this reagent. Smith and Bryant (5) were the first to recognize its possibilities and employ i t for analytical purposes. These workers avoided the problem of volatility and activity by employing it in the form of an acetyl pyridinium chloride suspension in toluene; in other respects their method was similar in principle to the acetic anhydride-pyridine procedures. I n this indirect use of acetyl chloride i t is probable that ketene (8) was the acetylating agent. Much would be gained if pure acetyl chloride rather than a suspension of acetyl pyridinium chloride in toluene were
used as the esterifying agent. This would eliminate the annoying pyridine vapors, the diluent and solubility effects of the toluene, and the use of a solid acetylating agent. I n order to use pure acetyl chloride a way must be found to measure and control it. Acetyl chloride reacts very slowly at low temperatures even with methanol; consequently solid carbon dioxide offers a convenient means of controlling its reaction rate. Linderstrom-Lang and Holter (1) have d e scribed an ingenious pipet for the precise measurement of small volumes. Using a modified form of this instrument, a simple technique has been developed for using pure acetyl chloride in determining the hydroxyl content of organic compounds.
Experimental REAGENTS. Acetyl chloride, Eastman (practical), sodium hydroxide, 0.3 N (carbonate-free),phenolphthalein indicator, and
dry ice.
822
Vol. 13, No. 11
INDUSTRIAL AND ENGINEERING CHEMISTRY
FIGURE 1. DIAGRAM OF PIPET
APPARATUS.The pipet illustrated diagrammatically in Figure 1 was constructed from 10-mm. Pyrex tubing, was 21 cm. over-all, and delivered 0.5 ml. of liquid. Its two important features were the 0.1-mm. constriction and the split rubber cap. By pressure parallel to the slit, the cap functioned as a medicine dropper. When a slight pressure was exerted in the opposite direction, the slit opened and the contents were then free to drain. The pipet was filled in the manner of a medicine dropper, the slit was opened, and the contents were drained to the constriction. The acetyl chloride could now be transferred to the reaction vessel. In delivery, by opening the slit, the contents of the pipet were allowed to drain into the lower capillary and then a slight pressure was exerted on the closed rubber cap, slowly forcing all the liquid out of the pipet. The reaction vessel (Figure 2) was constructed from a 20-cm. (&inch and a 10-cm. (binch) test tube. An inverted 15-cm. (&inch)) test tube fitted with a glass hook served to seal the water trap. ANALYTICAL PROCEDURE. Samples of 0.1 to 0.750 gram (depending on the compound) were weighed in a 10-cm. (4inch) test tube which in case of volatile materials was stoppered during the weighing. The test tube was then immersed in dry ice. After the charge was sufficiently chilled, a measured charge of acetyl chloride was added with the pipet and the small test tube was placed in a 20-cm. (8-inch) test tube containing 5 to 10 ml. of water, As indicated in Figure 2, a 15-cm. (6-inch) test tube inverted over the smaller test tube served as a seal. The tube was then stoppered and placed in a bath a t 40' C. for 20 minutes. In many cases this was unnecessary, since reaction took place immediately on coming to room temperature.
After 20 minutes the reaction vessel was inverted to hydrolyze the excess acetyl chloride. The contents were carefully removed and titrated with standard sodium hydroxide, using henolphthalein as the indicator. A smafamount of alcohol was used to wash the last traces of ester from the reaction flask. The per cent of hydroxyl present was then calculated by means of the simple equation (Blank
- ml. of sodium hydroxide)
normality X 17 10 X weight of charge
X
-%
Because of the quality of acetyl chloride used and because its titer may change with temperature, it is necessary to make blank determinations simultaneously. These blank runs also serve aa a good check on the analyst's precision. Whenever fading of the end point occurred, the bsse was added in small increments (0.03 ml.) until the color persisted for 30 seconds.
Results and Discussion The results obtained with this procedure are given in Table I.
FIGUR 2 IC
OF ALCOHOLSAKD PHENOLS TABLEI. ACETYLATION
SO. of
Detns. Primary and secondary alcohols Methanol Ethanol Propanol-1 Propanol-2 Butanol-1 2-Methylpropanol-1 Butanol-2 Pentanol-1 3-Methylbutanol-1 Pentanol-3 Hexanol-1 Cyclohexanol 2-Ethylhexanol-1 Octanol-2 Lauryl alcohol Benzyl alcohol Furfuryl alcohol Cinnamyl alcohol Tertiary alcohols 2-Methyl ropanol-2 2-Methul~utanol-2 Benzopinaool
Substituted alcohols Ethylene chlorohydrin 1,3-Dichloropropanol-2 Terpenes Borneol Menthol Geraniol Linalool
Per Cent of Theoretical Hydroxyl Content
a
5 5
1
5 4 5
5
5
Interfering factor: 0 Poor end point unable t o titrate. b Reacts with evblved hydrogen chloride. Rearrangement.
99.04
1.2
49.0b 88.7: 3.5
1.9 2.4
98.8 99.1 99.0 99.0 93.4d
0.4 0.3 0.4 0.4 3.2
98.6 100.3 100.9 100.7 140.4' 131.01
No. of Detns.
Average Deviation
Average Deviation
Miscellaneous Lithium lactate Rochelle salt Citric acid Benzoin
3 3 3 2
102.2 65.8d 38.3d 124. I/
1.5 1.7 3.1 3.2
Phenols Phenol o-Cresol m-Cresol pCresol p-tctt-amyl pheno a-Naphthol 8-Naphthol Thymol Xylenol Catechol Hydroquinone Resorcinol Orcinol Phloroglucinol Pyrogallol
5 5 4 5 2 2 2 5 2 4 2 2 2 6 2
99.4 100.6 99.9 101.0 101.2 107.7: 110.6 99.5 99.3 100.1 98.2 98.7 9.: 0
0.2 1.1 0.2 0.5 0.1 4.5 5.5 0.7 0.3 0.5 0.3 0.3 1.4
98.7
0.8
5 5 5 3
99.7 137.2'
0.5 4.1
Substituted phenols Guaiacol Isoeugenol Vanillin p-Chlorophenol o-Chloro henol 2,4-Dichroro henol 3-Bromo-4- Renylphenol 2 4 6-TriioZ henol o:Nitronheno?
0.2 0.3 0.1 0.3 4.5 1.5
Per Cent of Theoretical Hydroxyl Content
0
101.0 99.2 96.5 100.6 8.1 100.9 103.1 100.0 9.5 1.6
0.4 0.5 0.1 1.3 1.1 2.1 0.9 0.5
a
I acid p-Hydroxyl benzoic! acid Methyl salicylate a-Nitroso-8-naphthol
d Solubility.
3.3 61.9 89.8 14.8
' Possibly ,addition with evolved hydrogen ohloride. ~Enolication.
4.3 6.5 3.1
November 15, 1941
ANALYTICAL EDITION
This method is rapid and lends itself to mass production methods. It has considerable applicability and gives as good a precision as older methods based on the use of an acetylating agent. I n the case of the phenols the results in general were superior. From the results in Table I i t is apparent that several limitations are imposed by the character of the molecule undergoing esterification. The effect of solubility in this connection has been noted by others (6). I n initial experiments with mannitol low results were obtained. Whenasmall amount of water was added to this compound the acetylation was almost complete. The interference of several functional groups-for example, aldehyde and nitroso-with indicators was observed. This made titration by the usual methods impossible. Side reactions involving the liberated hydrogen chloride may account for several unusual results, particularly in the case of such olefinic compounds as geraniol, linalool, and isoeugenol, and may explain the unusual behavior of alpha- and beta-naphthols in which one ring readily forms addition products (7). The data obtained with tertiary alcohols can also be explained on this basis, since such alcohols are known to react readily with hydrogen chloride (7). Interesting observations were noted in the studies of the substituted phenols. As indicated in Table I, the more
823
acidic phenols such as picric acid were not acetylated. This was to be expected, as the hydroxyl group is more acidic than phenolic in character and therefore behaves as an acid (7). The failure to acetylate salicylic acid and its isomers cannot be adequately explained on this basis; perhaps it is more a question of chelation. It is evident that such factors as solubility, chelation, unsaturation, enolization, and rearrangement are important in determining the hydroxyl content of organic compounds by the use of acetyl chloride.
Literature Cited (1) Linderstrom-Lang, K.,and Holter, H., Compt. rend. trap. Eab. Carlsberg, 19, No. 4 (1931); 2.physiol. Chem., 201,9 (1931). (2) Marks, S.. and Morrell, R. S., Analyst, 56,428 (1931). (3) Normann, W.,and Schildknecht, E., FeUchem. Umchau, 40, 194 (1933). (4) Peterson, V. L., and West, E. S., J. Biol. Chem., 74,397 (1927). (6) Smith, D.M., and Bryant, W. M. D., J . Am. Chem. Soc., 57,61 (1935). (6) Verley, A,, and Bolsing, F., Ber., 34,3354 (1901). (7) Wertheim. E.,“Textbook of Organio Chemistry”, Philadelphia, P. Blakiston’s Son & Co., 1939. (8) Williams, R. J., “Introduction to Organic Chemistry”. p. 576, New York, D.Van Nostrand Co., 1935. PUBLIEHED with the approval of the Monograph8 Publioatiom Committee, Oregon State College, as Research Paper No 49, School of Science, Department of Chemistry.
A Method of Installing Tube-Wall Thermocouples E. L. PATTON AND R. A . FEAGAN, JR., United States Department of Agriculture, Naval Stores Station, Olustee, Fla.
Rietschel (6) installed the thermocouple junctions in grooves in the wall of a pipe or tube and brought the leads out in grooves covered over with litharge and glycerol cement. Reiher (6) and Colburn and Hougen (3) also used a groove installation and depended on litharge and glycerol cement for insulation, although the leads were finally brought out through the hot vapors. McAdams (4) gives an excellent discussion of the measurement of surface temperature, citing the literature on the subject. ColBaker and Mueller ( 2 ) used an installation similar t o that of Colburn and Hougen, in that a groove was cut three quarters of burn and Hougen (3) also discuss the errors resulting when therthe distance around the tube and the junction was installed in a mocouple junctions are installed directly on the surface or when drilled hole at the end of the groove. The leads were sealed into the leads are brought out through a medium either hotter or the groove and finally c:trried out through the hot vapors. Varicolder than the junction. All workers agree that it is advisable ous methods of sealing the lead wires into the groove were tried to bring the leads from the thermocouple junctions through a Substantially isothermal zone (as through the metal wall itself by Baker and Mueller who state that “pure Bakelite varnish plus a filler had a tendency to shrink and crack in service. Litharge rather than through the fluid stream), but McAdams states that the difficulty of construction has probably prevented wide use of and glycerol cement disintegrated. Lithar e and glyperol cement this method. with a covering of the Bakelite varnish a%o failed. ’ This was probably due to the fact that they condensed vapors of organic compounds as I I well as steam. In the method finally . ANY DESIRED DISTANCE adopted, they enclosed the leads in small JVNCTION brass tubes and sealed them intothegrooves BRASS TUBE A-1 with solder which was polished until flush -~-..-~--------------~ - - - - - - _ - - _ _-_-_._.---,__ _ _ _ _ with the surface of the heat transfer tube. However, the leads were brought out of the condenser shell through the hot vapors. Akin and McAdams ( 1 ) installed thermocou le junctions in holes drilled tangential& in the wall of the heat transfer tube and insulated the lead wires with Pyrex capillary tubing.
T
HE determination of heat transfer coefficients through liquid films requires a method of measuring tube-wall temperatures.
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FIGURE1. DETAILS OF INSTALLATION
I n investigating the heat transfer coefficientsfor the condensation of mixed vapors of turpentine and water on a single horizontal tube, the authors sought a method of tube-wall thermocouple installation which would meet the following stipulations: (1)lead wires to be brought out entirely through a substantially isothermal zone; (2) no insulation to be exposed to turpentine, which readily attacks and softens litharge-glycerol cement and similar materials; (3) con-
