V O L U M E 26, NO. 6, J U N E I 9 5 4
1089
proper choice of cut points, cyclohexane, methyleyelohexane, and total CScyclohexanes (excluding 1,l-dimethyloycloheusne) have been determined in petroleurn fractions. In addition to its use in the lower maleoular weight range, the dehydrogenation method may he extended to the Cr range and higher. Decahydronaphthalene, a dicyclic, has been quantitatively dehydrogenated in the presence of n-decane. There are, however, two complications to be considered when the method is applied t o the higher range: The possible number of gemsubstituted cyclohexane isomers increaaes rapidly, so that the reactable cyclohexane8should not be confused with total cyclohexanes, and there is at present no independent method for checking the ac-
curacy of results. The few results obtained so far have appeared to be logical, but further investigation is needed. LITERATURE CITED
(11 Am. Sac. Testing Msterials. "ASTM Standards on Petroleum products and LI.L.:---'" n o m c 1cm 3 3 , n r n (2) .'bid., Designstion (3) Tiarriz. C. G., Hc
communication. (4) Rampton, H. C.. P
RECE~VED for review September 17. 19G3. locepted February 2G, 1954. Presented at the Meeting-in-~liniatureof the Philadelphia Seotion of the .A,rnnrC.~N CHEMICAL SOCIETI. January 27, 1953.
rature Refractometry with an Abbe-Type Instrument E. P. BLACK, W. T. HARVEY, and S. W. FERRIS Sun Oil Co.. Marcus Hook, Pa.
- - _..
. J index
1 measurements have been used O l l r G * L l V L n W U VY UIC: l Y a b l U 1 1 9 1 UUI*&.U VI UbLLIIUaIUP, &llU \\~aS of petroleum wares, found to agree, after emergent stem correotion, uithin 0.1" a t there has been little uniformity in testing temperatures. Many 212mF, wax technologists have used 176" F. (80"C.) since 1929, fallowing Temperature-Control System. The water jacket of the refractometer wm connected to a source of low pressure steani and llie suggestion of Ferris, Cowles, and Henderson (S),who reported colinked with a I-liter water tank in such a way that,either water refractive indices at that temperaturein oonnection with their from the tank or steam could be admitted to the jacket. The work on the composition of paraffin wax. Until recently 176" F. unter tank wa8 equipped with 8. heater, was generally acceptable, since it fulfilled a primary requisite of ITater from the jacket outlet was recirculakd, but the steam maintaining any available petroleum TVZX in the molten state. Lately, hou.ever, many petroleum waxes are being produced that melt in the neighborhood of 200" F. and, consequently, 176" F. is no longer adequate for general wax refractometry. The temoerature 212' F. is niieeested herewith BR R suitahle ~.~~ ~.~~ .~~~~~ i,eniperature for refractive index measurements, since it exceecIS the melting point of any current petroleum wax product and it is conveniently attainable by the use of low pres~uresteam 8.8 a. heating medium. The adaptation and use bf an Abhd-type r(?frnctorneter for 212' F. refractometry is described below.
A-riim ~ " yyears far the &racte"zatiou
~
~~
~~~
__~
~~~~~
~~~
~~
~
APPARATUS
Refractometer. The instrument shown in Figures 1 and 2 was manufactured by the Valentine Technical Instrument Carp. and is designat,edas the Improved Precision model. In order th,t tem~ f L , ~ . ~EO.no Y7 ~ ~ ,~~ ~~ ~~ 7~ ~ , .: ~ ~-I ~ ~ ~ . . . L . . ~ ~ -
~~~1~~~
~
L
. ~ ~ ~ ~ ,
In preparing the instrument for use, the tank n,ater tva8 hentcd from room temperature to 200" F. while being circulated through the jacket to raise the prism temperature gradually, thus avoiding the damage by thermal shock that is likely to result from too rapid heating. When the temperature had reached 200' F. or above, over a period of a t least 30 minutes, the u-ater was shut off m d steam a t about 1-pound gage pressure was turned on. After 5 minutes of Steam flow with the temperature remaining constant ( i 0 . l ' F.) the instrument was considered to he itt temperature equilidrium and ready for index determinations. The jacket temperature in this appamtus held well within + O . l ' F. for an hour or more. Although occaBiona1 drift of 0.1" or 0.2" \vas observed, it r a 6 too slow to he significsnt during
ANALYTICAL CHEMISTRY
1090 a n y one index determination. In any case, however, it is advisable to record the jacket temperature with each determination. Insulation of Refractometer. Initial potentiometric temperature measurements made on the uninsulated refractometer indicated a temperature differential of 6' to 8" F. between the steam-heated jacket and the sample. I n order to minimize local cooling and to provide satisfactory temperature control, t h e prism mountings were insulated as described below. Slabs of cork 0.25 inch thick were cut to fit the sides of the prism mountings, extending 0.25 inch beyond the perimeters. Slabs for the top, bottom, front, and back were cut to the width of the mountings. Thus, when the pieces were in place, the overlap of the side insulation furnished a surface for cementing the abutting slabs covering the other areas. It was, of course, necessary to make suitable openings for the light path, for the heating medium connections, for the thermometer well, and for the spindle. The covering for the entire left or spindle side of both prism mountings was a single slab, pieced together around the spindle, and fixed rigidly to the top prism mounting insulation. The covering of the front, bottom, and right side of the lower mounting was fastened to, and moved with, the mounting when it was opened or closed. The cork slabs were joined with Armstrong's No. 299 waterproof cement. Althou h this cement is slow drying, it is resistant to water. The c o d covering was coated with a thin layer of asbestos cement, which was in turn painted with a thin slurry of 1: 1 alundum powder and 40" B6. sodium silicate solution, This coat, when dry, served to form a strengthening crust over the structure. A final coat of white paint was applied t o the finished insulation.
1.333 1.332 1.331
advantageous to readjust the alignment of the prisms with respect to the refractive index scale in order to read correct values directly. The adjustment was made by reference to a glass test piece: n g = 1.5000. According to information furnished by the manufacturer, the refractometer was subject to a deviation of -0.7 X 10-6 in index reading for every degree (centigrade) rise in temperature. Therefore, if the instrument is to read correctly a t 212" F., it should register a value of 1.50053for the test piece a t 77" F., which happened to be the temperature of the instrument when it was adjusted in these experiments. The adjustment was accomplished by the following procedure: The refractometer was placed in reverse to the normal position. The body of the instrument was tilted slightly toward the operator, and the lower prism mounting was opened to an angle of about 110" with the upper mounting. The test piece was fixed to the exposed face of the upper prism with a drop of monobromonaphthalene, the polished side against the prism and the polished end downward. A square of white paper was placed against the exposed face of the lower prism mounting to divert light from the source, placed above, into the lower end of the test piece. A sharp field division appeared in the telescope. The field division was set a t the center of the cross hairs. The scale arm was loosened by turning the set screw that grips the arm to the spindle. The arm was then shifted with reference to the spindle until the hair line observed through the microscope coincided with the reading 1.50053. The arm was set in this position by tightening the set-screw. The accuracy of the setting was tested by proceeding as in a normal refractive index determination-that is, a series of readings was taken, until a t least four were recorded that agreed within 0.0002. Since the averaged readings fell somewhat more than 0.0002 below the desired reading of 1.50053, a fine adjustment was made by setting the hairline of the microscope a t 1.50053 on the scale, and shifting the cross hairs in the telescope to bring their center to the field division. The cross hairs were shifted by turning the Allen set-screw on the side of the telescope barrel.
1330
An alternative and more direct method of adjustment can be used where suitable index standards are available with known refractive index a t 212' F. (The Sun Oil Co. has supplied n-Hexadecane and cis-Decalin as standards for cooperative tests, but arrangements are in progress to transfer this service to one of the nationally known research institutions.)
1.329
w 1.325
?
40 4
0.
ti
The refractometer, placed in normal position, is raised to working temperature, and the standard substance is placed in the space as in normal testing. The field division is placed at the cross hair intersection as accurately as possible and the sector scale is adjusted as described above. The correct setting for the sector scale can be calculated as follows:
1.321 1.323
a
Scale reading
+ c (212 - t )
nZk2
where,
t = observed jacket temperature, ' F.
1.3 I 9 13i e
4.317' 60
=
'
I
eo
"
"
100
120
"
"
160
140
I
'
"
ieo
"
c = temperature coefficient of refractive index The value 0.00025 is applicable to pure n-hexadecane or CisDecalin if (212 - t ) is not over 15" F.
200
JACKET AND SAMPLE TEMPERATURES TEMPERATURE,
Figure 3.
4
F
Data from Tests with Water
Light Source. A sodium arc lamp was used as the light source, as it permitted the removal of the compensating prisms, and thus allowed more room for insulation and for positioning the prisms. Furthermore, it afforded an advantage in standardization, since most published values are given for the D line of sodium. ADJUSTMENT OF THE REFRACTOMETER
It is standard practice to construct refractometers to read accurately at 68' F., and it follows that readings made a t any other temperature are subject to a temperature correction. When, however, an instrument is to be used routinely for determinations of index a t a temperature differing considerably from 68" F., it is
Tests with Water. The sample temperature was determined under test conditions by relating the refractive index of water, as observed in the modified instrument, to the corresponding temperature derived from published data. The data of Tilton and Taylor (6) are considered to be of the highest order of dependability but are limited to the range 59' to 140" F. On the other hand, the data presented in the Chemical Rubber Publishing Co. Handbook ( 4 )cover the range from 57' to 212" F., although the source is not given. The two sets of data, portions of which are plotted in Figure 3, are, however, in fair agreement with each other in the i w g e covered by both. The maximum disagreement a t any point is 0.0001. This is within the limit of accuracy of ordinary laboratory work, although it may be a significant deviation for precision work. The agreement is such, however, that the use of the handbook data a t 212" F.as a standard appeared justified.
1091
V O L U M E 26, N O . 6, J U N E 1 9 5 4 Test data were obtained with a 30% heart cut from redistilled water. In each of three tests, index readings were started as soon as the prisms were closed on the sample, and were continued without pause, with an alternating up and down approach to the cross hairs, as long as enough water remained to give a readable field division. Average readings after temperature equilibrium was established, were, respectively, for the three tests: 1.31769, 1.31767, and 1.31765. The average of these, 1.31767, was accepted as the determined value of nb. The jacket temperature was 213.8' F. The sample temperature was computed from the above data by the equation: t = 212
from a number of index observations on the Eykman instrument over a range of temperatures: For n-hexadecane (75" to 216" F.) =LOD
F.
1.45044
- O.O002317L(' F.)
For cis-Decalin (156' to 288' F.) n l oD
F.
= 1.49697
- 0.00023645 - 0.000000028t2
Values for n g 2 calculated by these equations are, respectively, 1.4013 and 1.4456.
+ nh -
C
where c = temperature coefficient of index = -0.000164/0 F. This was calculated from stated values for n208 D .4O andnE2'. Substituting the value determined in the instrument for n&, the calculation is:
t = 212
- 1.31783 = 213.00 + 1.31767 -0.000164
Since the jacket temperature was 213.8' when the data were taken, a gradient of -0.8" F. is demonstrated between the jacket and the sample. The sample temperature can also be determined graphically by extrapolation of the n D - t curve, Figure 3, to intercept the coordinate nD = 1.31767. The lines meet a t 212.9" F. as double circled in Figure 4, which is a detail of Figure 3, including only the area near 212" F. By this method the temperature gradient is shown to be -0.9' F. Correction of the jacket temperature by -0.8" or -0.9" to derive a true sample temperature is suggested by these data, but such a refinement is regarded as unwarranted in view of the uncertainty of the accuracy of the reference data.
0 0
0
0 0
0- D I S T I L L A T E W A X E S 0 - RESIDUAL WAXES
1.415
1.420
1.425
1.430
1.435
1.440
1.445
REFRACTIVE I N D E X AT 212.F
Figure 5.
Refractive Indices in Study of Petroleum Waxes
Refractive indices of the standards were determined with the Abbe instrument by each of four operators. Results for each sample agreed within 0.0002. The averaged results are given below, and compared with the Eykman values.
Eykman refractometer Abbe refractometer Deviation 208
210
212
214
TEMPERATURE, OF
Figure 4.
Detail of Figure 3
Tests with Pure Hydrocarbons. The accuracy of results obtained with this modified Abbe refractometer was established by testing samples of n-hexadecane and cis-Decalin representing the approximate extremes in refractive index encountered in petroleum waxes. The indices of these samples were determined by use of an Eykman refractometer giving results estimated to have accuracy better than 0.0002. Refractive indices a t 212" F. were calculated by the following equations which were derived
Refractive Index, 212' F. n-Hexadecane &-Decalin 1.4013 1.4456 1.4014 1,4454 +o. 0001 - 0.0002
The deviations are of opposite sign, indicating that average results are accurate. On the basis of the results obtained with water and with hydrocarbons, it was concluded that the temperature of the insulated jacket may be accepted as the sample temperature. PROCEDURE FOR ROUTINE TESTING
One or 2 drops of liquid sample (or an equivalent amount of solid wax) is placed in the sample space between the prisms. Temperature equilibrium is established in about 2 minutes. Several individual index readings are then taken in the customary manner, and a t least four of these, agreeing within 0.0002, are averaged to give a value for nb.
ANALYTICAL CHEMISTRY
1092 The refractive index, ma1*, is calculated from the equation: n i l 2 = n:
+ c(t
- 212)
where
rich in straight-chain compounds, while many of the others are essentially free of normal paraffins, and presumably of highly branched or cvclic structure.
jacket temperature in O F. (corrected for emergent stem) temperature coefficient of index for the sample For hydrocarbon waxes, the value of c is 0.000214 per O F. Corrections to 212" F. can be determined more conveniriitly by use of a table listing the calculated corrections, including emergent stem and temperature coefficient, fo; all thermometer readings from 210' to 214' F. a t intervals of 0.1 .
The authors wish t o acknowledge t,he assistance of J. L. Lauer aiid R . \V. King, who carried out the measurement of refractive intlez on piire hydrocarbons by means of the Epkman refrnctomrtt,r.
DISCUSSIOS
LITERATURE CITED
i = c =
This modified refract,ometer has been used routinely for over 2 years with no difficulties other than occasional damage t o the prism insulation or deterioration of rubber tube connections. Originally it was thought that the prisms would loosen or become clouded under high temperature conditions, making index readings difficult, but neither condition has yet been encounteretl. Figure 5 illustrates one method of employing refractive indices in the study of petroleum waxes. Values for normal paraffin hj-drocarhons fall on or slightly below the diagonal line. This liiie was established from literature data ( 1 , 8, 5) calculated to 212' F. The points are for substantially oil-free petroleuni waxes, and the position of each, with respect to the line, gives ai1 approximatr idea of the composition. Those close to the line are
ACKNOWLEDGMENT
(1) Do**, 11. P., "Physical Constants of Principal Hydrocarhons," The Texas Co.. 1933. ( 2 ) Fkloff, G . , "Physical Constants of Hydrocnrhona," 5.01. I. S e w York, Reinhold Publishing Corp., 1939. (:'I) r e r r i s . S. W., C o d e s . H. C . , ,Jr., a n d Hendehon. I,. 11.. Ind. E r ~ g Ckem., . 21, 1090 (1929). ( 4 ) H o d g m a n , C . D.. e d . , " H a n d b o o k of Chemidtry a n d Physics." 3 l s t e d . , p. 2279, Cleveland, Ohio, Chemical Ruhher Puhlishiog C o . , 1949. ( 5 ) Schiessler, R. W., et ul., "Synthesis a n d Propertie. of Hydrocarbons," API Project 42. (6) Tilton, L. K., and Taylor, J . K., J . Rrsrarch .\-ut!. Bur. Staridards, 20, 419 (1938).
R E C T I V Efor D review Xovember 21, 1953. Accepted A I a v h I?, 19.54. Presented before the Division of Petroleum Chemistry at t h e 1?4t!L LIeeting of the A M E R I C A N CHEMICALS O C I E T Y , Chicago, 111.
Spectrophotometric Determination of Vicinal Glycols Application to the Determination of Ribofuranosides JONATHAN S. DIXON and DAVID LlPKlN D e p a r t m e n t o f Chemistry, Washingtan University, St. Louis,
A
,
STASDARD method for the determination of viciiiul glycol groups in organic compounds is the oxidation of a weighed sample by a known amount of periodate followed by a volumetric determination of the excess periodate ( 3 ) . The work reported in this paper demonstrates that the consumption of periodate by vicinal glycol groups may be followed spectrophotometrically by using the absorption band of metaperiodate which has a maximum at about 223 mp ( 2 ) . The advantages of this spectrophotometric determination of periodate consumption over the usual technique are twofold. First, the rate of the oxidation reaction niay be followed readily and the completion of the r~ action is ascertained easily. Second, the determination of vicimil glycol groups may be carried out on about 10-8 to 10-8 mole of sample. It is feasible, therefore, t o apply the method to thc. quantitative determination of such groups in materials whit-li have been separated by paper chromatography. Recently, :t method for c,arrying out such dptrrminations colorimetricalljw:ts described by Adelberg ( 1 ) . This colorimetric method illvolves considerable treatment of the sample prior t o development of the final color and appears to be ICW accurate than the procedure described here. I n applying this procedure to the quantitative determination of vicinal glycol groups, several factors must be considered. One of these factors is the absorption of light by the products of t i l t s rcaction and the reactants. The product? formed in this rwction are iodate ion and compounds which may contain carbonyl or carboxyl groups. Fortunately, iodate ion has an extinction coefficient which is at most one tenth that of metaperiodatc, in tlic region 220 t o 240 mp and introduces no large error in the detc,rmination. Unconjugated carbonyl and carboxyl groups also do not interfere, but difficulties may be encountered in oxidations where products with conjugated carbonyl or carboxyl groups arc' formed. In contrasting thip procedure to the standard volu-
Mo. metric procedure, formic acid is oxidized to carbon dioxide and water by metaperiodate. This appears to be a photochemical reactioii which occurs in the light beam of the spectrophotometer. The spectrophotometric determination of vicinal glycol groups was (wried out on a variety of compounds. The data obtained with several ribofuranosides are summarized in Table I. The strong purine or pyrimidine absorption of the compounds listed in the table does not interfere with the determination. I n addition, the ahsorption spectra of the ribosides apparently are sufficiently like those of the corresponding dialdehydes produced in the osidation so that results of reasonable accuracy are ohtained. EXPERIMENT4L
Materials. rZ 0.1-If stock sol~itionof sodium metaperiodate iG. Frederick Smith Chemicd Co., Columtius, Ohio) was prpiiared and standardized by the usual procedure ( 3 I. .4portion of this s7lution was diluted to a concentration of 10-4.1f. The ribofuranosides, with the exception of the adenosine, were commercial samples (Schn-nrz Laboratories, Inc., Mount
'I'ahle I . Spectrophotometric Deterniination of Periodate Consumption b) Ribofuranosides Wave Length. mpa 227
Aloles ( X 10'1
Moles, f X,10') of Riboside
-ofPS!!odate
Coinpound -4dded Consumed Ratio' ;\dt,nosine 3 63 4.94 3 69 @.!a .idenosine-.5'phosphoric 227 0 97 1.U8 1 02 0.93 acid Guanosine 224 3 00 4.94 3 08 0 9Y 227 4 10 4.94 3 84 1 07 Cytidine I:ridine 230 4.l@ 4 94 4 09 1.00 " \Tart lcnath at xvhich disappearance of periodate was folloxed h hloles of riboside to moles of periodate consumed.
