THE HYDROXYLAMINE NUMBER Application to the Identification of Ketones ANTHONYM.TROZZOLOANDEUGENEL1EBER Illinois Institute of Technology, Chicago, Ill.
The “hydroxylamine number” is defined as “the number of milligrams of potassium hydroxide which is equivalent to the hydroxylamine required to oximate the carbonyl function in 1 gram of sample.” The present study, which is limited to pure samples of ketones of various structural types for which the hydroxylamine number is an invariant quantity, has demonstrated that the concept can be readily applied
I
N COURSES of qualitative organic analysis, aldehydes and
ketones are most frequently identified by the derivatives they form with hydrazine or one of ita substitution products (1.9). I t is, indeed, surprising in view of the many excellent, rapid, and accurate quantitative analyses of organic compounds via functional groups which are available ( 1 3 )that, pedagogically, practically the only methods applied in qualitative organic analysis are the time-worn, but very important, neutralization and saponification equivalents. To some extent we find even these simple quantitative tools neglected in emphasis upon the “solid derivative” for identification purposes. One of the authors (E. L.), in his classrooms, has striven to inculcate on the student the more quantitative aspects involved in the identification of organic compounds. The present paper is a summary of the application of the hydroxylamine titration of the carbonyl function to the identification of ketones and introduces the concept of the “hydroxylamine number” for such purposes. The present study is limited to pure compounds. The hydroxylamine number, in analogy to such terms as neutralization number, saponification number, iodine number, etc., is defined as “the number of milligrams of potassium hydroxide which is equivalent to the hydroxylamine required to oximate the carbonyl function in 1 gram of sample.” Because the functionality of a pure organic compound is an invariant quantity, the hydroxylamine number becomes as important a constant for the identification of a carbonyl compound as the preparation of an independent derivative. It thus can serve as an important tool in problems of the qualitative and quantitative identification of aldehydes and ketones. It is less time-consuming and more sparing of material, because micro and semimicroprocedures can be used. The determination of the hydroxylamine number of a carbonyl compound will enable an analyst to compute the equivalent weight of the compound. If the compound has been characterized previously, he may check ita identity as determined by the classical method or, if the compound is new, may compare the equivalent weight to the molecular weight as measured by the simple and rapid Rast procedure (12). The requirements for the identification of a pure organic compound must also be based on physical constants, spectra, or other “fingerprint” data peculiar to a particular compound. One usually has such knowledge prior to the preparation of a solid derivative or the determination of ita hydroxylamine number, and thus isomeric carbonyl compounds-e.g., valeraldehyde, diethyl ketone, methyl ethyl ketone, e t c . - c a n be differentiated and identified. With such a priori knowledge it is often possible to ident,ify carbonyl compounds in mixture without isolation.
to problems in the qualitative and quantitative identification of ketones. It presents an effective teaching aid in courses in qualitative organic analysis. It is applicable to simple and complex ketones. Internal interferences due to steric factors, cyclization with formation of isoazoxalones, conjugated unsaturation, and hydrogen bonding have been studied and are discussed. and applied by them to the determination of aldehydes and ketones in essential oils. Published in an obscure journal, the concept introduced by Stillman and Reed has found no application such as pointed out in the present paper and has never been used for instructional purposes in courses of qualitative organic analysis. This early paper (16)contains an excellent and detailed review of the hydroxylamine titration as known up to that time. More recent studies on volumetric oximation procedures have been published by Sabetay (10),Martin and co-workers (6), Siggia (1S),and Mitchell and co-workers (6),the latter employing the Karl Fischer reagent in conjunction with hydroxylamine. Oppenauer ( 8 )has applied the hydroxylamine titration in following the reaction velocity of the dehydrogenation of cholesterol to cholestenone, and Light ( 4 ) for the determination of carbonyl compounds in bile preparations. Byrne (2) has recently developed an interesting procedure for the determination of micrp quantitiea of acetone based on the change in pH caused by the liberation of hydrochloric acid by reaction with hydroxylamine hydrochloride, the method depending upon the calibration of a standard curve.
Table I.
Stability of Hydroxylamine Reagent 0.05 N HC1
Age Of’Reagsnt, Days 0 3 10 15
Required, M1.‘ 30.75 28.75 27.15
20
26.25
18.83 15.75
‘For 50 ml. of reagent. Table 11. Dialkyl Ketones, Cyclic Ketones, and Polyketones Hydroxylamine Number
%
Struoture Compound Acetone CHaCOCHi Diethyl ketone CIHICOC~HI Di-n-butyl ketone CIHBCOCIHB Methyl iaobutyl CH,COCHrCH(CHa)r ketone CHaCOC CHa)a Pinacolone 9-Heptadecanone C 8 H n ~ ~ b ~ , r Cyclohexanone m-Msthylcyclohexanone
YHr(CHx)xCH(CEL)CHrCO
CHaCOCHrCOCHa Acetylacetone CHa(CHa)&OCOCHa Acetylcaproyl CsHiCOCHrCOCHa Benro lacetone 12 1 3 - L a c o a a CuHraCOCOCiiHra hione 0 Calculated for two carbonyl groups. b Stable onmation value.
HISTORICAL
The concept of a hydroxylamine number is not new. This was expressed as a “carbonyl value” by Stillman and Reed (16) in 1932 764
Calcd. Found 965 966 651 645 394 388
deviation 0.14 0.92 1.52 0.36 0.54
572
559 558 219 579
500
497
0.6
1120° 789” 692”
1132 781
0.25
307’
809
0.65
581 561 220
410)
0.45
1.2
1.07
..
V O L U M E 2 2 , NO. 6, J U N E 1 9 5 0
765 hydrochloric acid present, while the acid titration will show the amount of hyd r o x y i a m i n e . These two quantities should be equivalent, or approximately
Table 111. Keto Esters, Keto Carboxylic Acids, Hydroxyketones, and Unsaturated Ketones Hydroxylamine Number
-
Compound Ethyl acetoacetate Ethyl n- ropylacetoacetate Ethyl a-yauroyl laurate Ethyl aeetonedicarboxyiate Ethyl benaoylscetate Ethyl benaoylformate Bensoin acetate Ethyl levulinate &Benzoyl propionic acid Diacetone alcohol Benzoyl carbinol Benzoin o-H droxyscetophenone p-$droxypro iophenone 2-Aceto-1-napgthol Benzalacetophenone Cinnarnalacetophenone Dibenaalacetone Dieinnamalacetone Furfuralacetophenone
Structure
Calcd. 431 325 142 277 292 315
221 389 315 483 412 264 412
CaHrCH=CHCOCaHr
L-00 4-hour reflux. b 7-hour reflux. reaction at room temperature.
C
374 301 270 239 239 196 283
Found 435 327 145 274 291 5 310.5 2190
390 318 477 408
70
0.95
260.5
409 377 301b 270 242.5c 288e5d
198
285C
CHCOCsHi 2-hour reflux. 4 1-hour reaction at room temperature.
so.
ALCOHOLICPOTASSIUM HYDROXIDE. When required, 3.60 grama of potassium h droxide are dissolved in 600 ml. of 9 5 d e t h y l alcohol (formula 30 may be used). STANDARD HYDROCHLORIC ACIDSOLUTION. Approximately 0.05 N aqueous hydrochloric acid is carefully standardized by the usual procedures. BROMOPHENOL BLUEINDICATOR. Onetenth gram of tetrabromophenolsulfonphthalein is round in a mortar with 3 ml. of 0.05 #sodium hydroxide. When solution is complete, the mixture is diluted to 25 ml. with water. PREPARATION OF H Y D R O XLY AMINE REAGENT.Nine g r a m of hydroxylamine hydrochloride are dissolved in 40 ml. of water and the solution is diluted to 800 ml. with 95% ethyl alcohol ( d e natured, formula 30). T o this solution are added, with stirring, 600 ml. of ethyl alcohol containing 3.6 grams of otassium hydroxide and 10 ml. of bromopienol blue solution is then filtered through a rapid filter
deviation 0.93 0.62 2.06 1.09 0.17 1.43 0.91 0.26 1.24 0.98 1.33 0.73 0.80
0.00 0.00 1.46 0.21 1 02 0.71
~~~~~~
indicator. The recentyears a number of interesting methods have been devised for the identification of aldehydes and ketones, making use weighed (see of a “quantitative number” approach. Smith and Wheat ( 1 4 ) calculations for method of estimating the size of sample to be used; this depends upon the carbonyl content) and transferred to a estimated the hydrazine nitrogen of semicarbazones iodomet. 250-ml. “iodine-type’’ stoppered flask (it is convenient to use rically by the Jamieson method (s). Seaman and c,,workers (1 such flasks equipped with standard-taper joints to fit a bank of deacribed the determination of 8-dicarbonyl compounds based on correspondingly equipped water condensers). Because semimicrothe formation of a copper complex and iodometric titration of the quantities are being used, great care should be taken i n this operation. The more volatile liquids Should be weighed in excess reagent after extraction of the complex with chloroform. sealed ampoules aa described b Niederl (7) and crushed below the Veibel (lo, r ) indirectly made use of a neutralization equivalent reagent; solids should be transzrred by the usual “charging-t#ut)e” by conversion of the carbonyl ComPoWd to the PcarboxYPhenYltechnique or by small glass cups, which are used for the less hydrazone and subsequent titration of the free carboxyl group volatile liquids. The size of the sample should be adjusted to yield a titration value between 10 and 15 ml. of the standard hydrawith s&ndard alkali. Petit ( 9 ) precipitated the carbonyl cornchloric acid. Fift milliliters of the hydroxylamine reagent are pound a pnitrophenylhydrazone and reduced the into the and the are thoroughly agitated, nitro group in the presence of an excess of standard s t m m ~ ~ A blank determination on 50 ml. of the reagent is also made. chloride or potassium stannite and titrated the excess stannous Sample and blank are vigorously refluxed for 1 hour under waterion with sgndard iodine solution. These methods, though interesting, cannot compare in Table IV. Aromatic Ketones and Keto Steroids simplicity with the direct hyHydroxylamine Number droxylamine titration. Compound Structure Calcd. Found % deviation EXPERIMENTAL
The experimental procedure adopted in the present paper was modeled essentially on that of Stillman and Reed ( 1 5 ) . However, because their macromethod used inordinately large samples (1 to 3 grams), a semimicroprocedure has been developed for the present purpose. Reagents. HYDROXYLAMINE HYDROCHLORIDE. This should be of best quality and contain little or no free hydrogen chloride. The purity of the reagent should be tested by d i s s o l v i n g a small weighed quantity (0.10 to 0.20 gram) in water and titrating with standard alkali to the phenolphthalein end point, and then with acid to the bromophenol blue end point. The alkali titration will show the total
Acetophenone Benzophenone Desox benzoin P.p’-gimethoxyhenzophenone facetophenone Benz
466 308 286 267
‘232 311
luorenone
374 386 340
Phenox acetone Benzoyraoetonitrile m-Nitroacetophenone
Cholestenone
469
296‘
283.6 266
233’ 309
0.65 3.57 0.87 0.75 0.43 0.65
385 339
a70
1.08 0.26 0.29
146
2.75
0
Methyl-3-acetoxy-12-ketodesoxycholate
7-hour reflux.
123
121
1.65
ANALYTICAL CHEMISTRY
766 cooled condensers, removed, cooled to room temperature under a cold-water tap, and titrated to the acid end point of the bromophenol blue indicator. As discussed under interferences, these experimental conditions will suffice to yield accurate results with a large majority of the carbonyl compounds. However, the presence of certain other functional groups or of steric resistance to oximation requires a modification of the general procedure here presented. This is amplified in the section on Results Obtained and in the discussion. Calculation. HYDROXYLAMINE NUMBER, Hydroxylamine number = ( B - 5”) X N H CX~ 56.1 weight of sample THEORETICAL VALUE. Theoretical hydroxylamine number = (56,108) X No. of CO groups molecular weight SAMPLE SIZE. atrHC1 x (10) x (56.1) Weight of sample = theoretical hydroxylamine number Calculated for ( B - T) g 10 where B is the value of the “blank” titration expressed in milliliters of standard hydrochloric acid and T is the sample titration. Materials Used for Test. The ketones used for testing the method were Eastman Kpdak White Label products, used without further purification. The keto steroids were independently prepared. Stability of Hydroxylamine Reagent. Inasmuch as a solution of free hydroxylamine is unstable, it was considered important to determine the keeping qualities of the hydroxylamine reagent. The reagent was prepared as described above and allowed to stand in a glass-stoppered bottle a t room temperature, and 50 ml. were titrated at intervals.
Table V. Variation in Hydroxylamine N u m b e r w i t h i n a Homologous Series for Ketones of Structure R-CO-R’ No. of Carbon Atoms
Molecular Weight
Calculated Hydroxylamine NO.
The data obtained are summarized in Table I. The strength of the reagent decreases to about 50% of its original value in 20 days. However, as blank determinations are conducted, this is of little importance. Over a pePiod of 1 week the titer of the solution remains very close to the original. Results Obtained. The results obtained are summarized in Tables I1 to IV, inclusive. The values reported represent the average of duplicate and triplicate determinations. DISCUSSION
The types of keto compounds thus far studied, asexemplified by Tables I1 to IV, may be classified aa simple dialkyl ketones, saturated cyclic ketones, keto esters, keto carboxylic acids, polyket,ones, aromatic and aralkyl ketones, hydroxyketones, ether ketones, unsaturated ketones, and keto steroids. Their estimation and identification by the determination of their hydroxylamine number are readily accomplished. The types of ketones to which this method of identification may be applied vary from very simple types to very complex substances. The average deviation for the forty-twp different compounds studied from the theoretical values is 0.98%. This average deviation from the theoretical makes the identification of a ketone within a homologous series certain because, as may be noted by a study of Table V, very large differences are obtained, especially for values below twelve carbon atoms, and even for very high molecular weight members
of seventeen and eighteen carbon atoms the differences ( 5 % between Cl, and CIS)are still beyond the average deviation from the theoretical values. Greater care must, of course, be exercised as the molecular weight increases and the carbonyl content of a compound becomes small. This should be taken so as to obtain a t least 10 to 15 ml. of blank minus titration values. Two general procedures have been developed in hydroxylamine titrimetry of carbonyl compounds, one being to add hydroxylamine hydrochloride reagent to the aldehyde and ketone and then titrate directly the liberated hydrochloric acid (IS); in the other method free hydroxylamine is used and the excess is titrated after the completion of the reaction. These two procedures are exemplified by the following general equations: RR’CO
+ NHZOH.HC1 RR’C=NOH + HCI + ”?OH +RR’C=XOH ----f
RR’CO
The latter has been selected as preferable, because standard hydrochloric acid is readily available for titration. The method avoids the difficulty caused by the presence of considerable acidity during the oximation, and the titration error due to differences in pH between the end point shown by the indicator and the true neutralization point of hydroxylamine hydrochloride is eliminated by a blank determination. As shownby Stillman and Reed (16), a hydroxylamine reagent comprising an equimolecular mixture of free hydroxylamine and hydroxylamine hydrochloride gives the best rateaof oximation and is the reagent employed in the present work. The free hydroxylamine concentration is such as to ensure its presence a t all times during the reaction and at the same time eliminates the danger of losing hydrochloric arid from a refluxing mixture of hydrochloric acid and alcohol. INTERFERENCES
Because the present study is concerned with pure compounds, the interferences are inherent in the compounds themselves and are not of the type which are met with in the analysis of mixtures of compounds or of impure types. The interferences that were actually encountered in the present investigation may be summarized as follows: (1) steric factors, ( 2 ) cyclization with formation of isoazoxalones, (3) conjugated unsaturation, and (4)hydrogen bonding. An expected interference due to the presence of carboxyl and carbalkoxy group, such as in keto acids and keto esters, with the formation of hydroxamic acids: RCOOR’
+ 1L;HZOH
----t
RCONHOH
+ R’OH
was not met. In order to test this more thoroughly, pure samples of ethyl acetate and ethyl oleate were refluxed over varying periods of time up to 7 hours. In all cases, the blank titration and the sample titration were within 0.05 and 0.10 ml. of each other, indicating that, under the conditions of the analysis used, no hydroximation of the carbalkoxy group takes place to form a hydroxamic acid. As will be noted from Table 111, keto estere and keto carboxylic acids show no such internal interference and good agreement between theoretical and experimental hydroxylamine numbers can be obtained. The “steric factor” appears to be a much more serious internal interference and is occasioned by the proximity of bulky groups about the carbonyl group. Diary1 ketones are particularly resistant to oximation, although other factors may be operative. This is illustrated by the data presented in Tables IV and VI, While benzoin is oximated smoothly, the introduction of an acetoxy group materially decreases the rate. and this decrease in rate is very much enhanced by replacing alkyl groups by aryl groups as illustrated by acetophenone and benzophenone. The separation of the aryl and keto groups by a methylene link immediately removes this interference, as may be noted by comparing benzophenone with desoxybenzoin (Table 111). However, fluorenone, the cyclic analog of benzophenone, offers no such interference and is oximated smoothly. This is in general true for
767
V O L U M E 2 2 , NO. 6, J U N E 1 9 5 0 Table VI. Compound Structure Oximation minutes lour lours lours lours
Benzoin CaHnCHOH
Benzoin Acetate CIHICHOICCH~
CsHrC=O
C~HIC=O
I
Acetophenone CaHaCOCHt
Benaophenone CaH,cOCsH
101 9s: 8
66:2
..
13.0 83.4
..
99.2
..
95:s
I
ditions. This can be avoided and the oximation directed solely to the carbonyl group by carrying the reaction out a t room temperature; varying times of reaction are required depending upon the particular compound under consideration. However, as in the case of the @-diketones, the higher temperature oximation appears to reach a conA n t value. This is illustrated by a study of the rate of oximation of dicinnamalacetone
Interferences from Steric Factors
81.8
..
.
..
0
/I
CH=CHCH=CHCCH=CHCH=CH all cyclic- ketones (Table I I ) , even those of a complex nature as illustrated by the keto steroids (Table IV). The interference of cyclization with formation of isoazoxalones is met with in the oximation of the @-diketones. Thus an unsymmetrical @-diketone can give rise t o two isomeric isoazoxalones:
Reflux, Hours 1, room temp. 7, room temp.
@
$RCOCH=C(OH)R~
L A
-3 RCCH=CR’
II
S-0
I
the controlling factor being the extent of enolization of the diketone which, as t o be expected, will depend upon the structure of R and R’. The data of Table I1 indicate that acetylacetone is osimated under conditions in which no enolization is encountered, inasmuch as the expected hydroxylamine number, based on the presence of two carbonyl groups, is realized experimentally, whereas benzoylacetone shows the presence of considerable enolization. However, in spite of this interference, it can be established that the experimental oximation value represents a stable value and thus can be utilized for identification purposes. Thus a measurement of the rate of oximation of benzoylacetone (CRH5COCH2COCH,) under various conditions shows the following: Reflux, Hours 1, room temp.
1
2 4 a
?& Oximationa 58.6 59.4 59.8 49.6
Based on two CO groups
demonstrating the constancy of its experimental oximation value. The interference caused by unsaturated conjugation is complex and is due t o a number of simultaneous reactions that take place, both at the carbonyl group and with the conjugated system comprising a double bond and a carbonyl group. These reactions depend upon the particular compound and the conditions under which the reaction is carried out. Thus Auwers and Muller ( 1 ) showed that benzalacetophenone reacts with hydroxylamine in alkaline medium as follows, forming:
45.8 101.0 137.3 169 2 169.2
1 2
4
RC(OH)=CHCOR’ 4RC=CHCR’
RCOCHzCOR’
% Oximation
Thus these highly conjugated carbonyl systems can be approached by either a room temperature oximation or under conditions of reflux. Interference due to hydrogen bonding could be expected in the aromatic series with the o-hydroxy substituted ketones. However, of the types studied (Table 111)this has not been realized and has been met with only in the case of 2-aceto-1-naphthol. This is illustrated by a comparative study of the rates of oximation of t h a t compound with o-hydroxyacetophenone: % Oximation o-Hydroxyacetophenone 2-Aceto-1-naphthol H / 0 0
‘..
1 2 7
99.3
..
52.2 58.2
100.0
Intermolecular hydrogen bonding, which theoretically could be met with in other types of hydroxyketones, apparently offers no interference to the oximation process. CONCLUSIONS
The hydroxylamine number is an invariant quantity for a pure compound and can readily be applied to problems in the qualitative and quantitative identification of ketones. It presents an effective teaching aid in courses of qualitative organic analysis. It is applicable t o simple and complex ketones and a systematic study of a large variety of different structural types is presented. The keto group in keto acids and keto CsHsCCHZC0CeH5CeH5CHCHzCCeH5 esters can be estimated without interference by hyI1 I /I dtoxamic acid formation. Although some p-diketones KOH NHOH NOH NHzOH undergo cyclization to isoazoxalones, they have experiCeHjCH=CHCOCsHs -+ OHmentally constant hydroxylamine numbers which can CsH5CCHzCCeH6C6HsC=CHCC6H5 be utilized for their identification. Interference due /I II to highly conjugated systems can be utilized in the 0I-Tu’ 11 NOH NOH same way, although by conducting the oximation a t among other products. However, as will be noted from Table 111, room temperature the carbonyl group alone is oximated. Hydrogen bonding appears to offer interference only in isolated under the conditions of oximation employed, benzalacetophenone gives excellent agreement between theoretical and experimental cases. hydroxylamine number calculated on the basis of the oximation of the one carbonyl group only. Furfuralacetophenone gives the LITERATURE CITED same result, but a %hour reflux period is required. However, in (1)Auwers, H.V., and Miiller, H., J . p7akt. Chem., 137, 57 (1933). the case of the more highly conjugakd system such as cbna(2)Byrne. R. E.,Jr., ANAL. CHEM.,20, 1245 (1948). malacetophenone, dibenzalscetone, and dicinnamalacetone, the (3) Jamieson, G. s., volumetr trio Iodate Methods,9pp. 36, N~~ Auwers-Muller types of reactions take place under reflux conYork, Chemical Catalog Co., 1926.
760
ANALYTICAL CHEMISTRY
(4) Light, A. E., IND.ENG.CHEM., ANAL.ED., 14, 42-3 (1942). (5) Martin, M. E., Kelley, X.L.,and Green, M . W., J . Am. Pharni. ASSOC., 35, 220 (1946). (6) Mitchell, J., Smith, D. M., and Bryant, W. M. D., J. Am. C h e m Soc., 63, 573 (1941).
(7) Niederl, J., and Niederl, V., “Micromethods of Quantitative Organic Analysis,” New York, John Wiley & Sons, 1942. ( 8 ) Oppenauer, R. v., Rec. t m u . chim. PaUS-BaS, 56, 142 (1937). (9) Petit, G., Bull. doc. France, 1948, 141. (10) Sabetay, S.,Bull. 8oc. chim. (51, 5. 1419 (1938). (11) Seaman, W., Woods, J. T., and Massad, E. A., ANAL.CHEW, 19, 250 (1947). (12) Shriner, R. L., and Fuson, R. C., “Systematic Identification of Organic Compounds,” p. 168, New York, John Wiley & Sons, 1948.
(13) Siggia, S., “Quantitative Organic Analysis via Functional Groups,” New York, John Wiley k Sons, 1949. (14) Smith, G. B. L.,and Wheat, T. G., IND. ENO.CHEM.,ANAL.ED., 11,200 (1939). (16) Stillman, R. C., and Reed, R. M., PerjuumeTy Eeeent. Oil Record, 23,228 (1932). (16) Veibel, E., A c h Chem. S c a d . , 1, 54 (1947). (17) Veibel, S.,Blaaberg, A., and Sterns, H. H., Damk Tids.F a n . , 14,184 (1940). RECEIVED November 14, 1949. Presented before the Division of Analytica and Micro Chemistry a t the 116th Meeting of the AMERICAN CHEMICAL SOCIETY, Atlantic City, N. J. Based upon a portion of a senior research project submitted by Anthony .M. Trociolo in partial fulfillment for the degree of bachelor of science, Department of Chemistry, Illinois Institute of Technology, January 1950.
Double-Beam Infrared Spectrophotometer Chemical and Biochemical Applications JOHN U. WHITE1 The Perkin-Elmer Corporation, Glenbrook, Conn. The value of a versatile double-beam recording infrared spectrophotometer in solving chemical problems is illustrated with several examples. Reproductions of original records show the advantages resulting from high speed, resolution, stability, and flexibility in the measurement of spectra, analysis of samples, and determination of structure. The possibility of compensating for scattering losses in mulls and for solvent absorption in solute study is particularly useful.
I
N T H E past the utility of infrared spectroscopy in chemical problems has increased directly with the ease of reducing the observations to useful form. Even though the uniqueness of infrared spectra has been known for many years ( 6 ) ,the necessity for point readings and curve plotting limited its use to university research and more recentb t o simple industrial analyses with point reading instruments (6). With the advent of commercial automatic recording spectrometers ( 4 ] .14, 16, IT), infrared spectroscopy became easy and fast enough for general industrial w e . The records obtained were useful directly for identification and analysis, but had t o be replotted on some absolute scale for easy understandability in conferences and publications. To avoid this labor of replotting, instruments have now been designed to record directly in graphs of uniform wavelength or wave-number scales us. per cent transmittance ( 1 , 8, IS, 18, bf, $8). When these features are combined with the high resolut,ionand versatility of modern instruments (8)i t is possible t o record directly a number of typa of spectra that would otherwise be difficult and time-consuming to measure. The purpose of this paper is t o show how such an instrument may be applied t o a group of diversified chemical problems. Many of them have been donebefore onsingle-beaminstruments, but without the ease and directness of the present work. Special attention is paid t o the advantages obtainable from the use of the doublebeam principle under a wide variety of operating conditions. I n each case the application is presented rn a brief description with reproductions of instrument recordings of per cent transPreeent address, The W h i k Development Corpomtion, 90 Linooln Ave., Stamford, Conn.
mittance us. wave length. The problems considered and t h e special features illustrated are: Type
Of
Stiy:2re
Spectra of isomers Product purity
Steroid spectrum
Example o-Toluidine
Features Illustrated Speed, noise level, and scattered light a- and pconidendrin Resolution, compensation for scattering 1% ethylbenzene in Elimination of styrene specstyrene trum by compensation DehydroisoandrosElimination of solvent specterone in chlorotrum form
f
Figure 1. Optical Layout and Block Diagram
