filtration would not interfere. various amounts of arsenic wcrp added to acidif i c d portions of the filtrate and the arm c n a p then generated. The results in the second half of Tahle I V show no interference 1)y any residual cobalt or, again, by the molybdenum. Results for cobalt-alumina-molybdena catalysts bv this method were also compared with those obtained by the arsenic trichloride diitillation method (6) (Table V). PLATIXX. I n processing catalysts containing from 0 A to l.OYc platinum, up to 500 y of platinum had been found in the filtrate after the initial basic filtration. T o measure the extent of interference from this amount of platinum. arsine was generated from solutions containing chloroplatinic acid. Severe interference $\-as observed (Fig-
ure 3). Therefore, the extraction of the last traces of platinum as the stannous chloride-platinum complex n as incorporated into the procedure. R e u l t s on typical platinum-bearing cata1,vsts are given in Table V. i l s ~ 1 a r o ~ ; r The . only likely interference in the color development is from stibine, which forms a red color with maximum ahsorbance near 510 mp. The sensitivity for antimony a t 540 mp is only about 8’3 that of arsenic. Thus far, interfering amounts of antimony in petroleum stocks or catalysts have not been detected. LITERATURE CITED
(1) Albert, D. K., Granatelli, L., ASAL. CHEK31, 1593 (1959).
( 2 ) Harkins, W. D., J . Am. Chem. Soc’
32.518(19101. , (3) Jay, R. R:, Dickson, L. R., Petrol. Processing 9 , 371 (1954). (4) Liederman, D., Bowen, J. E., hIilner, 0. I., ANAL.CHELI. 30, 1543 (1958). (5) Maranowski, S . C., Snyder,_R. E., Clark, R. O., Ibid., 29, 353 ( 1 9 0 , ) . (6) Powers, G. K., Jr., Martin, R. L., Piehl, F. J., Griffin, J. AI., Ibid., 31, 1589 (1959). ( i ) Sandell, E. B., “Colorimetric Drtermination of Traces of Metals,!’ 2nd ed., Interscience, New York, 1950. (8) ShiDman. G . F.. Afilner. 0. I.. ANAL. CHEX 30, 210 (1958). (9) Vasak, V., Sedivek, V., Chem. itsty 46, 341 (195%). -
\
~
RECEIVEDfor review May 27, 1959. Accepted September 16, 1959. Division of Petroleum Chemistry, 136th Meeting, ACS, Atlantic City, K. J., September 1959.
Determination of Hydroxyl Value of Alcohols by Near-Infrared Spectroscopy R. 0.CRISLER and A.
M. BURRILL
Miami Valley laboratories, The Procter & Gamble Co., Cincinnati 31, Ohio
b A method is described for the determination of hydroxyl value of aliphatic primary alcohols which uses the hydroxyl-stretching overtone band at 1.4 microns in the near-infrared region. Samples are analyzed as dilute solutions in carbon tetrachloride or tetrachloroethylene. Using a calibration curve, results on a number of fatty alcohol samples are compared with values obtained by the acetic anhydride-pyridine method. The standard deviation is 0.27 in the range 85 to 115 mg. of hydroxyl per gram of sample. Some differentiation between types of hydroxyls can b e made using the overtone region. Extension of this method to other alcohols, particularly tertiary and others difficult to acetylate, is suggested.
T
problem of determining the hydroxyl (OH) value of fatty alcohols using the OH stretching overtone a t 1.4 microns was undertaken as part of a n investigation of the usefulness of near-infrared spectroscopy. K i t h the availability of commercial near-infrared recording spectrophotometers of high accuracy and resolution, such a method might have material advantage in both time and applicability over the several n e t chemical methods currently in use. I n particular, HE
the applicability to tertiary and other alcohols that can be acet,vlated only with difficulty makes such a method attractive , The overtone band has been used in studies of hydrogm bonding ( 1 . 2, 6) and for specific analyses, such as the determination of hydroxyalkyl aniline in alkyl anilines (8)and the unncetylated hj-drouvl content of cellulose acetate (6). Hoaevcr, no stud>- of its usefulness for the determination of hydroxyl value has been presented. Ka! e. in his comprehensive review (4) suggests usr of the overtone region for the determination of alcohols in hydrocarbons and acids. I n the presrnt xork, near-infrared spcctra of a numbrr of fatty alcohols werr obtained a t several concentrations arid calibration curves prepared. H>droxyl values determined b y the near-infrared method on a number of commercial alcohols were compared with hydroxyl values determined by the acetic anhydride-pyridine method
(3,Y). I n the fats and oils field, hydroxyl value is defined as the milligrams of potassiuni hydroxide equivalent to the OH content of 1 gram of sample. As this definition has little meaning in the near-infrared method, results have been calculated and reported as milligrams of OH per gram of sample.
APPARATUS A N D MATERIALS
Spectrophotometer. -4 Cary Model 14 spectrophotometer equipped with a n absorbance slide-wire v a s used. Quantitative d a t a were obtained a t a scanning speed of 10 A. per second, and a t a slit-control setting of 15. T h e slit, width a t the analytical n a v e length was 0.1 mm., corresponding t o a 3.5-A. spectral slit width. T h e instrunient was swept a i t h dry nitrogen to reduce absorption by a t mospheric water vapor. T h e cells used were 10 cni. in lengt’h with sealed Corex end w i n d o w . Solvents. Baker analyzed carhon tetrachloride and Natheson Coleman and Bell tetrachloroethylene, industrial grade, were used as solvents. Both were purified by the addition of 0.5 pound of anhydrous silica gel per liter of solvent, shaking and filtering before use. Alcohols. T h e fatty alcohol standards used for calibration were middle cuts taken from t h e distillation of commercial alcohols. Their puritirs were established by gas-liquid partition chromatography and their hydroxyl values from replicate analyses using the acetic anhydride-pyridine method. Other hydroxyl compounds were commercial samples. For most of these, no purification was attempted; however. purities were estimated from gas-liquid partition chromatographic data. All VOL. 3 1 , NO. 1 2 , DECEMBER 1 9 5 9
2055
2.01 L
x
-
*
-
6
.
a m& 1.51.0-a
/@
/
100% O.km cell
1.0
1.2
1.4
1.6 1.8 Wove length, fi
2.0
2.2
rng. OH / rnl.
Figure 1. Near-infrared spectra of dodecyl alcohol in tetrachloroethylene
Table I. Comparison of Near-Infrared with Chemically Determined Hydroxyl Values
Hydroxyl.-i'alue, hfg. OH/G. Sample Chemical Nearcooperative infrared average Difference 90.9 90.8 0.1 85.0 84.6 0.4 111.4 111.5 0.1 115.4 115.8 0.4 104.3 104.3 0 91.4 91 4 0 90.3 90.0 0.3 Av. difTerence 0.19 Std. dev. 0.27
Table II.
Primary Alcohols Methanol 1-Butanol 1-Pentanol 2-Methyl-lbutanol 3-Methyl-lbutanol 1-Hexanol 1-Heptanol 2-Ethyl-1-butanol 2-Ethyl-1-hexanol Fatty alcohols Allyl alcohol Tetrahydrofurfuryl alcohol Benzyl alcohol 2-Phenylethanol 3-Phenylpropanol 2-Phenyl ropanol 2 4 2-MetEyl pheny1)ethanol 2-(4-Methoxy pheny1)ethanol Secondary Alcohols 2-Propanol 2-Butanol 3-Pent.ano1 1-Phenylethanol
2056
i/'
Figure 2. Calibration curve of aliphatic alcohols in tetrachloroethylene solution
are believed to be above 96 mole pure.
%
PROCEDURE
CAUTION.All manipulations involving carbon tetrachloride or tetrachloroethylene should be performed with care to avoid inhalation of the vapors or excessive contact with the skin. Calibration. Keigh amounts of standard alcohol (a pure dodecyl alcohol is satisfactory) equivalent to 25, 50, 75, 100, 125, and 150 mg. of OH into 50-nil. volumetric flasks. Dilute t o volume with carbon tetrachloride or tetrachloroethylene, and mix thor-
Near-Infrared Absorption Data
Molar Wave AbsorpLength of tivity, OH Liter/ Absorption, MoleMicrons Cm. 2.16 1.405 1.86 1.407 1.407 1.88 1,407
1.94
1.407 1.407 1.407 1.407 1,407 1.407 1.415
1.87
1 422 1,417 1,409, ,421 1,407 1,407, ,422
0.99 1.89 1.42 1.88 1.02
1.409, ,422
1.21
1,409, .422
1.11
1.412 1.411 1.410 1,416
2.17
ANALYTICAL CHEMISTRY
1.86
1.85 1.90 1.99 1.86 1.74
1.88
1.61 2.13
Molar AbsorpWave Length of tivity Liter/ OH Absorption, MoleSecondary Alcohols Microns Cm. l-Phenyl-2propanol 1.412, 1.424 0.99 1,2-DiphenyIethanol 1.417 1.54 2-Methylcyclohexanol 1.411 1.65 4-tert-Butylcy clohexanol 1.412 1.83 Borneol 1.411 1.91 Isoborneol 1.412 2.73 Menthol 1.412 1.62 Cholesterol 1 414 2.32 Tertiary Alcohols tert-Amyl alcohol a-Terpineol cis-Dihydroterpineol Phenols Phenol 2-Naphthol Isoeugenol p-Bromophenol 2-tert-Butyl-4methoxyphenol Thymol 2,6-di-tert-Butyl4-methylphenol
1,416 1.415
1.91 2.06
1.415
2.08
1.418 1.420 1.441 1,419
3.11 3.30 2.39 2.95
1.418 1,417
3.29 3.08
1,404
2.23
oughly. Fill a 10-cm. cell with t h e solution and record t h e spectrum from 1.6 to 1.3 microns, using a matched 10-cm. cell filled with the pule solvent as t h e reference. On the spectrogram, draw a background line tangent to the curve a t approximately 1.33 and 1.55 microns. Determine the corrected absorbance as the absorbance at the peak, 1.41 microns, minus the absorbance of the base line a t the same wave length. Plot the calibration curve using absorbance as the ordinate and concentration of OH in milligrams per milliliters as abscissa. Analysis. Keigh an amount of sample containing approximatply 40 mg. of OH into a 50-ni1. volumetric flask. Dilute t o volume n i t h carbon tetrachloride or tetrachloroethylene, and mix thoroughly. If n a t e r is present, add 0.5 t o 1 gram of anhydrous sodium sulfate, mix thoroughly, allox t o stand 15 minutes. and filter through coarse filter paper into a clean dry volumetric flask. Record the spectrum and determine the corrected absorbance of the solution as described. From the calibration curve, determine the hydroxyl content of the sample solution, and, by dividing by the sample concentration. the hydroxyl value of the sample. RESULTS AND DISCUSSION
The spectra of dodecyl alcohol in a 0.1-cm. cell and as a 1% solution in tetrachloroethylene in a lO-cm. cell are shown in Figure 1. The OH overtone band a t 1.41 microns and the combination bands a t 2.0 microns are apparent in the solution spectrum but are weak or missing in the spectrum of the pure material. Unlike the bands in the fundamental region, the bonded OH absorption is much weaker than the free OH absorption. The effect of hydrogen bonding on the calibration curve in tetrachloroethylene is shown in Figure 2. /Beer's law is obeyed only at low concentrations; however, as the calibration
curves for the alcohols octyl t o octadecyl are coincident u p to concentrations corresponding t o 2 mg. of O H per ml. of solution, a single calibration curve may be used and a hydroxyl value method is possible. The calibration curve obtained using carbon tetrachloride as the solvent is ideniical to the one shown in Figure 2 and this solvent may be used. Tetrachloroethylene is preferred, however, because of its lower toxicity, higher boiling point, and greater chemical stability. The chemical instability of carbon tetrachloride has caused difficulties in some analyses-for example, in various aliphatic amine solutions, the amine hydrochloride was formed and precipitated. The presence of water in the sample may cause some interference a t the analytical wave length. Tetrachloroethylene saturated with water when run us. dry solvent yielded an absorbance of 0.01 unit at the analytical wave length, corresponding to 0.01 mg. of OH per ml. The solubility of water in carbon tetrachloride is somewhat higher, corresponding to a possible error of about 0.2 mg. of OH per ml. This error can be eliminated by the addition of anhydrous sodium sulfate to the sample solution. A series of samples of commercial alcohols on which the chemical hydroxyl value had bern determined cooperatively by a number of laboratories was analyzed b y the near-infrared method (Table I). The precision, as determined by the difference between the near-infrared results and the chemical cooperative average and calculated as a standard deviation, is 0.27 in the range 85 to 115 Ing. of OH per gram of
sample. This is better than the standard deviation of the chemical method of 0.77 in the same range. Other Applications. Having shown the method satisfactory for t h e analysis of f a t t y alcohols, a brief survey of some other hydroxy compounds was made t o determine t h e general applicability of this approach. Table I1 shows t h e molar absorptivities and wave lengths of t h e peak absorption of these materials run under analytical conditions. The samples were run at one half the recommended concentrations (0.02 to 0.03M) and at twice these concentrations to confirm the absence of appreciable intermolecular hydrogen bonding. The lower concentrations correspond to the linear part of the calibration cbrve for fatty alcohols. As could be expxted, the band positions and intensities are dvpendent on the structure of the compounds. The OH overtone band shows a shift to higher wave length in the order primary-secondary-tertiary phenol. In the series of primary alcohols, a consistent increase in molar absorptivity is observed for the branched alcohols, the values increasing as the position of branching approaches the 1 positicn. The relatively wide variation in absorptivities of the secondary alcohols is related t o the appearance of nonsymmetrical absorption peaks. These are probably indicative of the presence of intramolecular hydrogen bonding, although the presence of impurities not resolved in the chromatographic analysis must not be ruled out. The presence of a n intramolecular hydrogen bond has been established ( 2 ) in the compounds for which two absorption
maxima are listed in the table. In these compounds, the absorptivities are reported for the major absorption peak. The phenols exhibit a wide variation in absorptivity and wave length. These variations a n be explained to some extent by consideration of the various effects of the other substituents on the aromatic ring. From this table, it can be seen that :L single calibration curve cannot be uscd for all OH-containing systems. Fortunately, in most cases, the nearinfrared procedure can be successfully used after suitable calibration data are obtained. Such an application might be the determination of hydroxyl value of a family of essential oils in which the hydroxylic constituents are the same. LITERATURE CITED
(1) Bellamy, L. J., “Infrared Spectra of Complex hlolecules,” p, 83, Wiley, New York. 1954. ( 2 ) Goldman, I. AT., Crider, R. O., J . Org. Chem. 23, 751 (1958). (3) Hafner, P. G., Swinney, R. H., \Vest, E. S., J . Biol. Chem. 116, 601 (1936). (4) Kaye, R., Spectrochim. Acta 6, 257 (1954). (5) Mitchell, J. A , , Bockman, C. D., Jr., . 29, 499 (1957). Lee, A. V., r l x . 4 ~CHEM. (6) Pauling, L. “The Nature of the Chemical Bond,” p. 316, Cornell Univ. Press, Ithaca, N . Y., 1940. (7) West, E. S., Hoagland, C. L., Curtis, G. H., J . Bio2. Chem. 104, 627 (1934). (8) Whetsel, K. B., Robcrson, IT. E., Krell, 31. W., .&SAL. CHEJI. 29, 1006 (1957). RECEIVEDfor review June 8, 1959. Accepted September 11, 1059. Presented in part a t the Pittsburgh Conference 011 Analytical Chemistry and Applied Spectroscopy, March 1950.
Chromatographic Separation of Fatty Acids Based on Chlorophenacyl Esters ANDRE C. KlBRlCK and S. J. SKUPP. Biochemistry Section, iaboratory Service, New York Veterans Administration Hospital, New York, N. Y
b 4’-Bromo-2-chloroacetophenone has been synthesized from acetyl chloride and monochlorobenzene. Esters of decanoic, lauric, myristic, palmitic, stearic, oleic, linoleic, and linolenic acids have been prepared with this reagent, and melting points and absorptivities a t 257 mp are reported. The separation of the eight fatty acid esters b y chromatography on a column of polyethylene and Celite and elution
with various proportions of alcohol are presented.
T
HERE was a need for a definitive
chemical method for the quantitative determination of fatty acids in blood and tissues. Chromatography, both paper and column, had but a limited success in separating the higher fatty acids, especially the unsaturated
acids. The principle of isotope derivative dilution has been applied to the determination of amino acids of protein hydrolysates by Keston, Udenfriend, and Cannan by the use of p-iodophenylsulfonyl chloride (6). Other reagents have been proposed for amines (9), alcohols (fO), steroids ( 8 ) , and sugars ( 3 ) . The 4’ - bromo - 2 - haloacetophenones are a class of reagents that seemed VOL. 31, NO. 12, DECEMBER 1959
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