948
INDUSTRIAL A N D ENGINEERING CHEMISTRY
Sherrard and Blanco.2 I n order to eliminate the gelatinous condition of the cellulose the material was digested in w a k r on a hot water bath for varying periods. The cellulose could then be washed with water and filtered easily. This is in accord with some of the later results by Sherrard on the partial hydrolysis of wood cellulose. The hot water-soluble content was reduced, progressively, to approximately 1 'per cent, as shown in Table 111. TABLE 111-EFFECT
OF HEATINGREDWOOD-HEARTWOOD CELLULOSEIN WATERBATHPOR VARYING PERIODS OF TIME BEFORE FINALWASHING (Results on basis of oven-dry weighti Hot watersoluble content of total Heating Total cellulose periods cellulose Per cent Hours Per cent 42.9 7.9 1/2 42.7 6.5 1/Z 42.4 1 4.0 3.0 1 42.4 2 42.4 0.8 0.6 2 42.5 1.6 2 42.5 2 42.3 1.3 1.0 2 42.2
Samples of cellulose prepared by the regular method (with high hot water-soluble content) and others prepared by the modified method (with low hot water-soluble content)
Vol. 16, No. 9 ...
were boiled with water 20 min-Utes, filtered, and the residues and filtrates terJted for traces of acids. The moist residue from cellulose with high hot watersoluble content gave a distinct acid reaction on remaining in contact with blue litmus for a few minutes. The filtrate from the same cellulose, on oxidation with bromine water and the addition of barium chloride, Droduced a white precipitate insoluble in hydrochloric acid: These two tests [ndicate that some sulfur dioxide remained on the cellulose and some was taken up by the water on boiling. The presehce of sulfur dioxide with the cellulose a t temperatures of 100" to 105" C . during drying would cause hydrolysis and the subsequent appearance of hot water-soluble material. The moist residues from cellulose with low hot watersoluble content (prepared by the modified method) showed no test for acid with litmus. The filtrate from the same cellulose on oxidation with bromine water developed a very slight cloudiness. The advantages gained by a slow digestion of the cellulose with hot water can be stated as follows: (1) The elimination of the undesirable gelatinous property of the cellulose is accompanied by facility in washing and filtering. ( 2 ) By a more thorough removal of acids and salts, a more highly hot waterresistant product is obtained.
Titration of Aniline and Homologs' By D. 0.Jones and H. R. Lee THENEWPORT Co., MILWAUKE~, WIS.
HE usual nitrite titrations of aniline, 0-and p-toluidines, and xylidine require a t,emperature of 0" to 5" C. on account of the instability of the diazo compounds. The slow rate of diazotization of these amines makes their analysis by this method both tedious and inaccurate. This investigation was startedto determine whether the principle of the back titration method,2 as applied to the analysis of dehydrothio-p-toluidine, could be applied to this class of compounds. PRELIMINARY TITRATIONS Preliminary titrations made on a sample of purified p-toluidine yielded low results. In these titrations a sufficient quantity of the amine to require approximately 40 cc. 0.1 N sodium nitrite solution was diluted to 400 cc., 25 cc. concentrated hydrochloric acid added, the solution cooled to 0" C., and approximately 10 cc. excess of 0.1 N nitrite added. Back titrations were made after allowing to stand from 2 to 5 minutes. The results indicated at once that a longer time would be necessary for complete diazotization. Upon extension of the time allowed for diazotization, in the presence of the excess nitrite, a maximum absorption was reached in 30 minutes. The values corresponding to this nitrous acid absorption were, however, over theory, which suggested a loss of nitrous acid. A measure of this loss is shown in Table I. The expression 3 HN02z=*HN03 2N0 HzO, commonly given for the decomposition equilibrium of nitrous acid in solution, suggested the use of nitric acid for suppressing the loss of nitrous acid in this titration.
T
+
+
1 Presented before the Division of Dye Chemistry at the 66th Meeting of the American Chemical Society, Milwaukee, Wis., September 10 t o 14, 1923. 2 Lee and Jones, "An Accurate Method for the Analysis of Dehydrothio-*-toluidine," presented before the Division of Dye Chemistry at the 66th Meeting of the American Chemical Society, Milwaukee, Wis., September 10 to 14,1923. (See page Q30,this issue.)
TABLE I-Loss No. 1
2
OP NITROUS ACIDFROM SOLUTION AT O' C. 0.1 N NaNOz , $-NITROANILINE USEDsolution taken Immediate titration Titrated after 30 min. cc. cc. cc. 10.00 10.11 9.85 10.00 10.11 9.80
STABILITY OF NITROUS ACIDSOLUTIONS The stability of nitrous acid solutions of different concentrations was then studied. Solutions containing different quantities of 0.1 N nitrite in a volume of 400 cc. containing 25 cc. concentrated hydrochloric acid were allowed to stand at 0" C. for various lengths of time with and without nitric acid present, and the nitrous acid remaining was then titrated with p-nitroaniline solution. The results are shown in Table 11. TABLE1I-sTRBILITY O F NITROUS ACIDSOLUTIONS Time allowed to stand with HNOs used @-Nitroanilinesolution excess nitrite before back tiNo. Cc. used in back titration tration-Min. Part la-10 cc. 0.1 N NaN02 taken 10.20 1 None IO.22 None 2 None 4 5 10.25 10.22 4 10 5 None 6 None 30 7 5 10.16 10.18 8 10 Part 2-20 cc. N a N & laken None 9 5 10 10 None 11 5 12 20 5 13 10 20.91 14 20 21.06 15 a IIIParts 1 and 2differentfi-nitroanilinesolutions were used.
:::;a
The presence of nitric acid was found to have no injurious effect upon the diazotiqation reaction or upon the end point. I n Table I1 it is shown that check results are obtained with
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INDUSTRIAL A N D ENGINEERING CHEMISTRY
September, 1924
or without nitric acid if the back titrations are made immediANILINE-The technical product was redistilled three ately. Furthermore, 10 cc. nitric acid are effective in p r e - -times i n vacuo. The second ahd third distfllations gave venting the loss of nitrous acid by dissociation when 10 cc. products h a s n g a freezing point of -6.29" C., which corre0.1 N nitrite are allowed to stand a t 0" C. in a volume of sponded4to 99.92 per cent. 400 cc. for 30 minutes. For larger quantities of nitrite more A n a l y s i s by Nitrile. A 3.7115-gram sample was dissolved, nitric acid is required, 20 cc. excess nitrite requiring a t least diluted t o 506 cc., and 50-cc. aliquots taken. 20 cc. nitric acid. 0.1 N factor nitrite, 1.0684 An excess of approximately 10 cc. 0.1 N nitrite and the 0.1 N factor 9-nitroaniline, 10064 addition of 10 cc. concentrated nitric acid are therefore the D-Nitroaniline 0.1 N nitrite Aniline found Nitrite taken required consumed (m. w. 93.1) most suitable conditions. No. cc. cc. c c. Per cent Samples of the purified p-toluidine, previously referred to as 1 47.50 10.90 39.78 99.78 2 47.50 10.88 39.80 99 84 yielding low results in the preliminary titrations, were then 3 47.50 10.88 39.80 99.84 analyzed in the same manner except that they were allowed to stand for 30 minutes before making the back titration. TiXYLIDINE-A sample of technical m-xylidine was converted trations were made with and without nitric acid. The results into the hydrochloride, which was then recrystallized and are shown in Table 111. converted into the base. The base was distilled i n vacuo TABLE 111-ANALYSIS O F 9 - T O L U I D I N E WITH AND WITIIODT NITRICACID and a constant-boiling middle fraction taken for analysis. Without "Os P e r cent 100.Fj2 100.12 100.07
With 10 cc. "01 Per cent 99.72 99.92
Analysis by Nitrite. A 4.7620-gram sample was dissolved. diluted to 500 cc., and 50-cc. aliquots taken. 0.1 N factor nitrite, 1.0684 0.1 N factor $-nitroaniline, 1.0064 p-Nitroaniline 0.1 N nitrite Nitrite taken required consumed cc. c c. cc. 49.00 13.00 39.27 49.00 12.99 39.28
TIMEREQUIREDFOR COMPLETE DIAZOTIZATION The time required for complete diazotization of technical samples of aniline and homologs was then determined, using 10 cc. concentrated nitric acid and approximately 10 cc. 0.1 N nitrite in excess. The results are shown in Table IV. TABLE IV-DIAZOTIZATIONARTER VARYINGPERIODS OR TIMG Time allowed before back titration-Min. YO
$-Toluidine Per cent 98.15
20
99.20
30
99.40
45 Average cc. 0.1 N NaNOz present in excess f o r 30-min. titration, , ,
.. . .. . .
Aniline Per cent 99.54
Xylidine Per cent 98.51
99.75 99.78 99.72 99.78 99.78
99.01
99.40
o-Toluidine Per cent 98.78 98.78 98.83 98.74 98.88 9 8 . SI 98.81
10.53
10.53
11.05
11.21
98.63
99.01
The data clearly show that in all cases maximum nitrite absorption is obtained by allowing 30 minutes' standing before making the back titration. PRFPARATIONS AND ANALYSIS OF PURIFIED SAMPLES I n order to show that this method gives theoretical results for this class of compounds, pure samples of each were prepared and analyzed. p-Toi,uvrDIh-E-The technical product was recrystallized from alcohol, distilled, and sublimed in vacuo. The purified product had a crystallizing point of 43.57' C. A n a l y s i s by Nitrite. A 4,4979-gram sample was dissolved, diluted to 500 cc., and 50-cc. aliquots taken. 0.1 N factor nitrite 1.0432 0.1 K factor $-nitdaniline, 0.9964 --$-TOLUIDINE-
No. 1 2
Nitrite taken Cc. 50.00 50.00
$-Nitroaniline required c c. 10.19 10.23
Analvsis bv Kjeidahl 0.1 N nitrite Found nitrogen consumed (m. w. 107.11) (m. w. 107.11) cc. P e r cenit P e r cent 42.01 100.03 99.87 41.97 99.94 99.87
o-ToLuIDINE-The technical product was purified by the method of Rosenstieh1,s redistilled, and the constant boiling middle iraction taken for analysis. Analysis by Nitrite. A 4.0306-gram sample was dissolved, diluted to 500 cc., and 50-cc. aliquots taken. 0.1 N factor nitrite 1.0269 0.1 N factor 9-nitrdaniline, 0.9870
--
o-Toluidine found Nitrite $-Nitroaniline 0.1 N nitrite taken required consumed (m. w. 107.1) No. cc. cc. cc. Per cent 1 47.00 10.81 37.60 99.91 2 50.00 13.92 37.61 99.92 a Lunge, "Technical Methods of Analysis," Vol. 11, P a r t 11, p. 855.
No. 1 2
Xylidine found (m. w. 121.14) Per cent 99.90 99.93
METHODOF ANALusIs-Measure with a dry Mohr pipet or transfer-depending upon whether the sample is liquid or solid-a sufficient quantity of the sample into a tared weighing bottle, such that one-tenth of it will require approximately 40 cc. 0.1 N sodium nitrite solution, and weigh. Transfer to a 500-cc. volumetric flask, using 5 per cent hydrochloric acid to wash the weighing bottle; then dissolve by further addition of acid and dilute to volume. Pipet a 50-cc. aliquot into a 600-cc. beaker, dilute to 300 cc., add 25 cc. concentrated hydrochloric acid, surround with ice, and cool to 0" C. Add chipped ice to the solution and, while stirring, add 50 cc. 0.1 N sodium nitrite solution, then immediately add 10 cc. concentrated nitric acid (Nz03 free). Cover with a watch glass and allow to stand for 30 minutes with occasional stirring. Titrate back the excew nitrous acid with the standard p-nitroaniline solution, as described in the analysis of dehydrothio-p-toluidine.2 STABILITY O F THE 0.1 N p-NITROBXILINE SOLUTION-An approximately 0.1 N solution of p-nitroaniline was standardized daily against 10 cc. of a 0.1 N solution of sodium nitrite for a period of 16 days. Assuming that the nitrite solution was stable, no regular change occurred in the p-nitroaniline solution. The largest difference in the p-nitroaniline solution required for titration during this period was 0.15 cc. This was apparently due to different observations of the end point, for when these standardizations were applied to the analysis of a sample of sulfanilic acid by the back titration method on the corresponding days, identical values were obtained.
DISCUSSION OF THE METHOD Analyses of samples of commercial aniline by the freezing point method4have been in very close agreement and usually slightly lower than by the procedure herein described. This relation would be expected because of the presence of a small quantity of homologs. The method described is not only suitable for the analysis of aniline and its homologs in the pure state, but is especially valuable for technical samples, liquors, extractions from residues, etc., the amino values of which are frequently required in commercial work. 4
THISJOURNAL, 12, 882 (1920).
