Quantitative Analysis of Clay Minerals with the X-Ray Spectrometer GERHARDT TALVENHEIMO’ AND J. L. WHITE Lgronomy Department, Pr~rdueCnicersity, Lnfayette, Ind. The purpose of this work \cas to develop a semiroutine technique for quantitative x-ray diffraction analysis of clay minerals in synthetic and natural mixtures using the Geiger-counter x-ray spectrometer. A combination of preferred orientation and glycerol solvation technique was found to enhance the basal spacings and make possible differentiation between expanding and nonexpanding clay minerals. The following conditions were most suitable for the qualitative and quantitative analysis of the polycomponent system of kaolinite-illite-bentonite: calcium saturation, glycerol solvation, 5 mg. of clay per sq. inch of mount, and drying at 8% relative humidity. The procedure developed gives an accuracy within 5 to lo%, comparable to that obtained with camera-type diffraction units but requiring considerably less time. The method should be of value to workers in the petroleum and ceramics industries, soil scientists, and highway engineers.
T
HE application of the x-ray diffraction principal to the quantitative analysis of clay minerals in synthetic and
natural mixtures has received a great deal of attention in recent years. That no satisfactory semiroutine technique of x-ray analysis has been developed as yet is due t o a host of factorq, chief among which are the time-consuming nature of sample preparation, the proximity and variabilitv of the diagnostic basal spacings of various clay minerals, the long exposure time required for recording the diffraction maxima, and the initial expense of the u-ray diffraction equipment. A general outline of the preparation and analysis of clay minerals will more fully illustrate some of the difficulties encountered during this type of analysiq. A typical method consists of the following steps: preliminary purification of the clay minerals b\ sedimentation; fractionation into various particle size groups; saturation of the exchange complex with calcium or some other cation by the centrifugationdecantation-alcohol 1%-ashingprocedure; preparation of the clav niinrrnl mixtures and mounting them either as randomly oriented powdrrs or as oriented aggregates, exposure to x-radiation for 2 to 14 hours: and development of the film and measurement of the angular values and relative intensities of the (hkO) and (001) lines. This simplified scheme of analysis is characterized by the timeconsuming nature of each individual step. The scheme becomes extremely complicated when cognizance is taken of the variahilit?- of the c-axis spacing of montmorillonite (due to the effect of tation saturation and degree of h) dration) and of the coincidence of the vermiculite-chlorite and kaolinitr-chlorite basal spacings. It is evident from this brief presentation of the problem that the elimination of some of these lengthy procedures and the simplification of others are very much desired by those interested in clav mineral analysis, particularly when the accuracies of 5 to 10% ( 1 , 1 5 , 1 6 ) obtained do not appear t o justify the labor expended. The direct-reading Geiger-counter x-ray spectrometer is convenient for clay mineral analvsis. The outstanding features of this instrument are: The time required for obtaining an x-ray 1
Present address, Houdry Process Corp. Marcus Hook, Pa.
diffraction diagram is reduced from hours to minutes, errors inherent in film processing are eliminated, either randomly oriented powders or preferentially oriented samples may be used, the 28 values may be read directly from the goGometer quadrant, and the diffraction maxima can be permanently recorded directly on strip charts by a synchronized automatic Brown recorder, or the intensity of the diffracted radiation may be determined manually with a Geiger counter-scaling circuit arrangement. The sensitivity of this unit is very high and it has been reported to give 1 to 5% accuracies (6-7‘, 9 ) in the quantitative analysis of quartz, mica, and penicillin. The direct-reading Geiger-counter spectrometer is not a “cured”for the fundamental difficulties of clay mineral analysis, such as the variation of the composition of the unit cell resulting from random isomorphic substitution, the irregular superposition of lattice sheets, the occurrence within the mineral of randomly alternating sheets of different degrees of hydration, and the presence of intergrowths (in which two or more clay mineral species have their basal cleavage plates interstratified). But in conjunction with the glycerol-solvation technique of MacEwan (10, 11) for attaining a constant c-axis spacing value of montmorillonite, it does offer a means of attaining the rapid quantitative analysis of clay minerals with the same degree of accuracy as given by the camera-type diffraction units. The purpose of the following investigation was the development of such a method. It is recognized that the validity of the use of so-called “standard minerals” in preparation of standard curves for mineralogical analysis is dependent upon the degree of similarity between the “standards” and the corresponding minerals in the unknown. Characteristics 15 hich are especially important in this respect are the degree of crystal perfection and the particle-size distribution within a given fraction, MATER1 4LS
The Wyoming bentonite (Upton, Wyo.) was procured from thc American Colloid Co., Chicago, 111. It contains 90 to 95% montmorillonite and small amounts of feldspar, gypsum, and quartz. The illite (Pennsylvania underclay, Fithian, 111.) \ m e obtained from R. E. Grim, Illinois State Geological Survey, and has been reported to contain 15 to 25% quartz as an impurity. The kaolinite (Macon, Ga.) and quartz (Brazil) were obtained from Ward’s Xatural Science Establishment, Inc., S e n k’ork, h-.Y. The clay mineral localities correspond to those reported under Research Project 49 (1950) of the ilmerican Petroleum Institute. The clays were dispersed with 0.01 .V sodium hydroxide, the >2-micron fraction (largely impurities) was removed I n - sedimentation, and the remainder was fractionated into two pize fractions of 2.0 to 0.2 and -edwas the Korelco Geiger-counter s-ray qwctrometer Type 12021. The diffraction patterns w e 1 ~recorded on strip charts hy means of a Brown automatic recorder. The unit was operated with a n iron-target tubc a t 6 ma. and 35 ! i v l the radiation k i n g filtered by a manganese filter. The eyst ~ m of collimating slits was varied to w i t the particular needs of cx:ich series of experiments hut {vas kept constant within any one serir.s. Slit wttirigs were t l r n o t d l)y the following symhols: S I I 3 . etca.. for a n emergent s-ra?. heam of medium width and 0.003 irwh height arid G l I 3 , rtc., Cor a reflected beam of medium uidth and 0.003 inch h(4ght as woeived hy the Geiger counter. Sranning speeds of 2 and 1 r. p. m.were used for the qualitative and quantit,ativr studies, respectively. Preceding earh experimental wries the awuracy and reproducibility of the unit were “standardized“ hy comparison with the angular value and intensity of the 3.33 .1.diffraction line of the quartz sample supplied with the instrument. The d values of the clay mineral diffraction lines \\ere read directly from tahlcs supplied by the Socony-Vacuum Laboratories (14). The clay minerals were prepared for diffraction analysis employing the following technique. The clay suspension \vas pipetted directly onto a 2 sq. inch area previously delineated on a 1 X 3 inch glass niicroscope slide by lines 2 i n c h ~ sapart drawn slightly nith a wax pencil normal to the long axis of the slide. The suspension was effectively contained within the prescribed area by the surface tension forces operative between the suspension, glass edges, and wax lines. The clay mounts so prepared were air-dried and then stored over anhydrous calcium chloride. For x-ray diffraction analysis these slides were placed in the specimen holder, so that the plane of sedimentation of the clay partic.l(,s paralleled the incident beam of x-radiation. EXPERIMESTAL PROCEDURE
Concentration of Clay per Unit Area. Mounts were prepared from the dialyzed hydrogen-saturated coarse and fine kaolinite, illitme,and bentonite fractions such that t,he concentration of clay varied from 1 t o 25 mg. per sq. inch. Saturation with Various Cations. The lithium, sodium, potassium, ammonium, magnesium. and calcium clays were prepared by the batch technique, employing the corresponding chloride-free Amberlites. The method consisted of the single addition of ;Imbei.lite in a 10 t’o 1 excess (on a milliequivalent basis) to the clay suspension and measuring the amount of cationic exchange by pH determinations. The degree of saturation of the above clays was in the neighborhood of 80 to 100% ( 1 2 ) ; total saturation wit,h the various cations was not attained under these conditions because the equilibrium of the exchange reaction was in favor of the Amberlite and because of the relatively large amounts of cation required to bring about pH changes in the 6 to 7 region. Thus, a milliequivalent ratio of 10 to 1 (Amberlitebentonite) increased the pH from 4.5 to 5.5; of 20 to 1 from 5.5 to 6.6; of 40 to 1 from 6.6 to 6.7; and of 50 to 1 from 6.7 to 6.8. Hence to attain complete cationic saturation without using relatively large volumes of Amberlite, the latter must be added and removed in small amounts until the neutralization point is reached. This method approaches the column technique of Amberlite utilization and \vas employed to give total saturation of the calcium clays used for quantitative analysis. Solvation with Various Polyhydroxy Compounds. For the qualitative studies the glycerol, polypropylene glycols, niethylpentanediol, and hexahydric alcohols were added in excess (1 drop per 5 t o 50 mg. of clay) to the dialyzed hydrogen-clay fract,ions and to the various clays mentioned in the preceding section. -1queous solutions of glycerol and methylpentanediol (500 mg. per ml.) were quantitatively added by means of a microburet to the hydrogen-coarse bentonite and illite and the glycerol was also added t o the totally saturated calcium-clay fractions. The suspensions were allowed to solvate for 12 hours, with intermittent shaking. Relative Humidity Studies. The calcium-saturated, glycerolsolvated clay fractions were mounted directly in desiccators containing saturated aqueous solutions of ZnClz. 11/2H20 (10% R.H.), S a C l (30.5% R.H.), Ca(NOs)z.4H20 (51% R.H.), H2C20d.2H20 (76% R.H.), and ZnSOj.7H20 (90% R.H.) and permitted to dry.
Preparation of Working Curves. Because the clay minerals generally occur in close association with each other and accessory minerals such as quartz, the coarse and fine working curves were prepared from t,he polycomponent, systems of kaolinite-illitebentonite-quartz and kaolinite-illite-bentonite, respectively. The illite and bentonite were added to the systems by means of a microburet and the kaolinite and quartz by means of a pipet (their rapid rate of settling precluded the use of a microburet). From these suspensions clay mount’s were prepared in duplicate, dried a t 870 relative humidity, and stored a t the same relative humidity. The diffraction patterns were recorded automaticallv with a scanning speed of 1 r.p.m., the damping and amplitude rontrols set a t maximum, and both the collimating slit systems set a t a narrow beam width and 0.005 inch beam height. Automatic recording was employed in preference to the more precise inethod of manual counting in view of the time factor involved in counting four to five diffraction maxima over a range of 20” and also because in a relative study of this nature, in nhich the materials under investigation are the factors limiting the accuracy obtainable, any errors introduced as a result of mechanical lag would be incorporated into the working curves. The peak area of each diffraction maximum was obtained by joining the background preceding and succeeding the peak (with a French curve) and measuring the enclosed area with a planimeter. To minimize the error introduced by the differential absorption of glycerol, the working curves were based on mineral concentrations expressed on the dry basis a t 330’ C. for 4 hours. RESULTS AND DISCUSSION
Concentration of Clay. Increasing the amount of clay from 1 to 25 mg. per sq. inch of mount was equivalent to preparing a series of specimens ranging from the quasi-infinite to the finite in thickness. -4s the total amount of diffraction of x-rays is a linear function of the number of reflecting planes in the case of clay minerals, the intensity of the diffracted radiation will increase with the specimen thickness of planar mounts until limited by the absorption and extinction of the incident and reflected radiation. Experimentally, the “saturation thickness,” or the concentration of clay producing the maximum number of effective reflecting planes, was observed to be approximately 5 mg. per sq. inch, Below this value the integrated and maximum intensities of the diffraction maxima (as measured by the peak areas and heights, respectively) rose rapidly with increasing specimen thickness, whereas above it the increase per unit of clay added was relatively slight. The 1 t o 5 mg. per sq. inch range of linear proportionality, although intolerable of minor variations in clay concentration, is better suited to quantitative analysis than the 6 to 25 mg. per sq. inrh range because within it are approached the ideal conditions of a quasi-infinite specimen thickness, maximum sensitivity t o variations in concentration, and the minimum amount of absorption and extinction. Furthermore, the gelation of bentonite upon the addition of Aniberlite, the flocculation during measurement with a microburet, and t,he unequal distribution over the surface of a glass slide are avoided by employing very dilute clay suspensions. Hence, in the majority of the following studies, the 1 to 5 mg. per sq. inch range of clay concentration v a s employed. The “saturation thickness” of 5.0 mg. per sq. inch v a s used in the preparation of the working curves. Type of Cation os. Diffraction Maxima Characteristics. The results for the coarse and fine clay fractions were qualitatively identical; hence only the values for the former are presented in Table I. The angular position of the (001) line of kaolinite was constant irrespective of the type of cation on the exchange complex and the areas (integrated intensities) varied only slightly. These results are not surprising in view of the relative inertness (chemicallj-) of the kaolinite crystals, and the choice of the saturating cation, for quantitative analysis, would be determined by physical factors such as the degree of dispersion (lithium, sodium, potassium) obtained, etc. The monovalent cations in general intensified the (002) diffraction maximum of illite without appreciably changing the angular position and peak area. The divalent cations, on the other hand, resulted in a 0.4 t o 0.7 A. increase of the (002) line and a noticeable increase in peak area in the case of magnesium. The apex of
1786
Table I.
ANALYTICAL CHEMISTRY Influence of Type of Saturating Cation on Diffraction Maxima
(Kaolinite, 9 mg /sq. inch a t Xh14 GM5 Bentonite, 4.5 m ./sq. inch a t XRIB,'Gh14. Illite, 3.5'mg./sq. inch a t XM4, G a s ) Coarse Kaolinite Coarse Illite Coaree Bentonite Series Series Series Area, Area, Area. Cationa sq. in. 001 (A.) sq. in. 002 (.I.) sq. in. 001 (4.) Li 1.08 7.14 2.20 10.7 3.62 14 1 iia 1.06 7.14 2.20 10.9 3.07 12.8 K 1.03 7.14 2.23 10.7 2.19 12.8 KH4 1.15 7.14 2.48 10.9 3.17 12.8 H 1.12 7.14 2.49 10.6 2.18 14.2 1.12 7.14 2.80 11.3 4.00b 14.6 1.02 7.14 2.5G 11.3 4.00b 14.6 a 80-100% saturation except H = 100%. h Obtained b y extrapolation of chart.
t?
the peak extended from 9.8 to 12.4 A . in both instances (11.3 A. being the median value). The significance of the variability of the (002) line of illite is discussed in the section on polyglycol solvation. As regards the choice of the most suitable cation for the quantitative analysis of illite, the sharply defined peaks of the monovalent series would be better adapted to quantitativc. measurement than the broad peaks of the divalent series. In accordance with their effect on the peak area and angular value of the (001) diffraction maximum of bentonite, the cations may be placed in two groups: (1) those with a 2-layer configuration of water molecules separating the crystal lattices (lithium, magnesium, calcium) and large peak areas, and (2) those with a monomolecular configuration (sodium, potassium, ammonium) and small peak areas. The hydrogen ion is unique in that i t falls into both groups. The d values for the various cations are in excellent agreement with those obtained by the powder technique ( 2 , 8 ) . The enhancement of the (001) basal reflection attained in the first group, particularly with magnesium and calcium-saturation, is believed t o result from the higher degree of parallelism of the clay plates brought about by the presence of two oriented layers of water molecules, which in turn increased the preferential orientation of the bentonite crystallites. The absence of such enhancement in the hydrogen-bentonite is probably due to the presence of larger, more stable aggregates which would decrease the perfection of the orientation. The striking difference between calcium and potassium saturation was further investigated by varying the degree of saturation of these cations (Table 11). Table 11. Effect of Increasing Degree of Cationic Saturation on (001) Line of Fine Hydrogen Bentonite Cation Saturation,
(3.3 nig./sq. inch) K Seriesa
Ca Series"
% 6 12 24 36 6 12 Peak area, sq. inches 4.25 4.25 3.43 3.20 2.52 3.41 OOl(A.) 12.1 12.1 11.5 11.3 13.9 13.9 a K series a t X V 3 , GM4. Cn series a t XM1, GJI4.
24
36
3.75 13.Y
3.92 13.Y
The per cent saturation was calculated on an Amberlite-clay exchange efficiency of 10% for a single reaction (based on the determined efficiency of 10 to 15% for the Amberlite-l N salt solution systems) and the saturation values are necessarily relative in nature. The well-known "fixation" of the potassium ion and the ensuing contraction of the interplanar spacing become evident between 12 and 24% potassium saturation. Similarly, the effect of calcium saturation in increasing the peak area also occurs a t a low (6 to 12%) degree of saturation. As regards the quantitative analysis of bentonite, these experiments emphasize the undesirability of potassium as the saturating cation and that 100% saturation with calcium is not essential for attaining an optimum diffraction maximum. The difficulty of duplicating the angular values of the basal
spacings of the expandable types of clay minerals, under uncontrolled laboratory conditions, is well illustrated by a comparison of the values in Tables I to IV. With this rather serious obstacle in mind, the stabilizing influences of a number of polyhydroxy compounds were next investigated. Polyhydroxy Compounds us. DifEraction Maxima Characteristics. The hydrogen, ammonium, and calcium coarse and fine kaolinite fractions showed no alteriition of the (001) spacing position with polyhydroxy solvation. -411 the polyhydroxy compounds produced a decrease of the maximum and integrated diffraction intensities, as shown for calcium-kaolinite in Table 111. The absence of molecular m t e r between adjacent crystal lattices of the kaolinite explains the constancy of the (001) line. The physical adsorption of the polyhydroxy compounds on the crystallite surfaces of kaolinite is very likely and the decreased intensities observed may be the result of disrupted orientation of the crystallites or/and of x-ray nhsorption by the organic molecules. Table 111. Effect of Polyhydroxy Compounds o n Basal Spacings of Coarse, Calciuni-Saturated Clay Minerals Treatment Glycerol Polypropylene gib col
Kaolinite Illite Bentonite Area, Area, Area. sq. in. 001 (.i.) sq. in. 002 (.I.) sq. in. 001 (.I., 7.14 1.00 1.16 9.8 1.29 17.4
400 750 1200 2 Methylpentane-
0.77 0.96 0.86
7.14 7.14 7.14
0.88 1 05 1.17
9.8 9.8 9.8
1.40
1.58
18.8 16.8 17.1
2,4-diol Hesahydric alcohol
0.85
7.14
1.69
11.8
1.18
14.2
1.00 0.90
7.14 7.14
1." 0 1.01
9.8 10.0
1.23 0.84
18.2 18.2
1.83
~
Sorbo
Arlex
The reduction of intensities observed with the kaolinite fractions also occurred upon solvation of the potassium, hydrogen, and calcium illite fractions, the greatest decrease being obtained with potassium illite. Glycerol, the polypropylene glycols, and the hexahydric alcohols in effect dehydrated the illite fractions and the observed (002) spacing values were identical t o the dehydrated value of 9.8 A. for illite heated for 1 hour a t 500" C. Secondary reflections a t 12.4 to 13.6 h.,weak but distinct, were observed with glycerol, the polypropylene glycols, and to a lesser extent the hexahydric alcohols. These reflections were more pronounced with calcium illite than with hydrogen illite. The 2methylpentane-2,4-diol was unique in that it brought about the least reduction in peak area and the displacement of the (002) diffraction maximum to a value of 11.8 A. Brown ( 4 ) has defined illite as being a clay mica with a 10 =!= 0.2.4. first-order sparing which remains constant when the mineral is subjected to mild thermal or chemical treatment. It is obvious from the cationsaturation and solvation experiments that the material under study is not a true illite, a s was also observed by Nagelschniidt ( 1 3 ) . The experimental evidence suggests that it is a mixedlayer structure of illite and a regularly interstratified montmorillonoid type of mineral (the latter present in very small quantities as estimated from the relative intensities of the basal spacings). Thus, glycerol and methylpentanediol solvation of such a mixedlayer material would give theoretical intermediate spacings of 13.6 and 12.0 A., respectively (calculated from the illite and bentonite values obtained in this study), which values were closely approximated by the 13.6 and 11.8 A. values actually observed. The primary purpose of the polyhydroxy solvation procedure is the attainment of a constant c-axis spacing of montmorillonite which is also distinctive enough to permit its definite identification. These conditions were met by all the polyhydroxy compounds studied, with the exception of methylpentanediol (Table 111). The difference in the c-axis expansion of the glycerol and polypropylene glycol-solvated calcium bentonite (0.6 A . ) is not believed to be significant, as the latter compounds expanded the
V O L U M E 2 4 , NO. 11, N O V E M B E R 1 9 5 2 (001) spacing of magnesium bentonite t o 17.4 .4. T h e greatest increase between adjacent clay layers was brought about by the sorbitol-containing compounds, Sorbo and hrlex, which contain 70 and 80% sorbitol, respectively. Methylpentanediol, on the other hand, formed a complex with bentonite without expanding t,he adjacent clay layers and in this respect was similar to the ethoxypentamethylene glycol of Bradley (3). The ability of these polyhydroxy compounds t o increase the distance between adjacent clay layers does not appear t o be a function of the aliphatic chain length but appears t o be related to the number of hydroxyl groups per carbon atom of the chain and to the number of methylene links in t,he chain. Thus the data from Bradley ( 3 ) and this study indicate that maximum expansion occurs wit.h polyhydroxy compounds in n-hich the ratio of hydroxyl to carbon atoms (of the chain) does not esceed 1 t o 2 :ind in which the number of methylene groups of the aliphatic chain does not exceed 2. The question of whether or not these rehtioriships of clay complex formation and c-axis expansion are general for all polyhydrosy compounds would require and merit more experimental data than presented here. Although the sorbitols brought about the greatest expansion of the c-asis sparing of bentonite, the susceptibility of their clay corriplc~ser to microbiological attack prohibited their use in qu:tntit:itive analysis studies, for which glycerol was finally chosen. The relatively large reduction in diffraction intensity of the solvated clays as compared t o the nonsolvated indicated that solvation in excess would not be suitable for quantitative analysis by the preferred orientation technique as shown in Table IV. Similar rmults were obtained with the fine clays and also with the calcium-saturated clay fractions. The coarse and fine clays eniploj-ed for the quantitative stud?- m r e saturated with 0.5 and 1.0 mg. of glycerol per mg. of clay, respectively, although these quantities are not believed to constitut,e t,he minimum amounts rcquirtd for optimum solvation. Table 11.. Quantitative Addition of Glycerol to Coarse Hydrogen Saturated Illite and Bentonite" N g . Glycerol
nIg.
~
Illite in. 002 (.\,) 3.32 10.1
aArea, y sq.
~
0.0
1.94 1.67 1.06
0. 1.0
2 0
10.0 10 1 10.1
Bentonite 001 (.CY 1.78 14.4
.- the present study. Though the results given here do not represent those of a true illite, their inclusion ie justified on the basis of the great similarity of the characteristics of the basal plane reflections of illite, hydrous mica, glauconite, etc.
(1) .\Idrich, D. G., Hellman, S . S . , and Jackson, 11.L., Soil S c i . 57,215 (1944). ( 2 ) Rarshad, I., Am. Mineral., 35, 225 (1950). f.3) Bradley, IT.F., J . Am. Chem. Soc., 67, 975 (1946). (4) Brown, G., “X-Ray Identification and Crystal Structures of Clay Minerals,” G. 17.Brindle)., ed., p . 155, London, Taylor and Francis, Ltd., 1951. ( 5 ) Carl. H. F., -4m. Mineral.. 32, 508 (1947). (6) Christ, C. L., Barnes, R. B., and Williams, E. F., -4x.1~. CHEY., 20,789 (1948). (7) Dijke, B. S. ran, Am. Mineral., 34, 74 (1949). (8) Hendricks. S. B., Selson, R. A . , and Alexander, L. T., J . Am. Chem. Soc., 62,1457 (1940). (9) Klug, H. P., .\lexander, L., and Kummer, E., AXAL.C m h r . , 20, 607 (1948). (10) MacEwan, D. M. C., J . Soc. Chern,. Ind.. 65, 298 (1946). (11) RIacEwan, D. 11.C.. Trans. Faraday Soe.. 44, 349 (1948). (12) Marshall, C. E., “Colloid Chemistry of the Silicate Minerals,” Sew York, .\cademic Press, 1949. (13) Sagelschmidt, G., X i n e r n l o g . Mag.. 27, 69 (1944). (14) Socony-Vacuum Laboratories, R e p t . 48-14-5 (1948). (15) n’hiteside. E. P., and Marshall, C. E.. Jlo. .Igr. Exp. Sta., Research Bull. 386 (1944). (1B) TVillis. ;1.L.. Pennington. R. P., and Jackson, RI. L., Soil Sei. SOC.-4m.Proc., 12, 403 (1947).
R E C E I V Efor D review January 11, 1952.
Accepted September 6, 1962. Presented hefore the Eighth Annual Pittsburgh Diffraction Conference, XoT-eiiiber 1950. Journal Paper 594.
Analytical Acetylation Application to Coal Hydrogenation Products C. W. DEWALT, JR.’, AND R . 1. GLESR Coal Research Laboratory, Carnegie I n s t i t u t e of Technology, Pittsburgh, Pa.
T
HE interpretation of the data obtained when standard analytiral methods are applied to crude products from the drgraciation of coal is often difficult. The products obtained dircctly from coal hydrogenation are so complex and so little is linoa-n about their composition that organic group analyses have had a limited application in their characterization. The determination of hydroxyl groups by acetylation, Freed and Wynne’s procedure ( 8 ) , has been used routinely for several years in this laboratory in the study of coal hydrogenation oils, but results have not always been consistent and the cause of the lack of agreement has not been apparent. Therefore, this study was
* Present address, Mellon Institute. Pittsburgh, Pa.
undertaken Tvith a txofold end in viem-: t o obtain reproducible results in the analysis of these complex mixtures and to gain a wider knowledge of the scope of the acetylation reaction, particularly as applied to phenols. Acetylation by acetic anhydride affords a method for determining phenols, as well as primary and secondary alcohols, thiophenols, thioalcohols, and primary and secondary amines. A reactive hydrogen is replaced by an acetyl group in the acetylation of each type, as shopm in the following equations. The analysis for all of these types together, which the procedure under consideration is, may be called the determination of acetylatable hrdi ogen.
