ANALYTICAL CHEMISTRY
1092 The refractive index, ma1*, is calculated from the equation: n i l 2 = n:
+ c(t
- 212)
rich in straight-chain compounds, while many of the others are essentially free of normal paraffins, and presumably of highly branched or cvclic structure.
where i = jacket temperature in O F. (corrected for emergent stem) c = 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
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
"Physical Constants of Principal Hydrocarhons," The Texas Co.. 1933. Fkloff, G . , "Physical Constants of Hydrocnrhona," 5.01. I. Sew York, Reinhold Publishing Corp., 1939. rerris. S. W., C o d e s . H. C., ,Jr., and Hendehon. I,. 11..Ind. E r ~ g Ckem., . 21, 1090 (1929). Hodgman, C. D.. ed., "Handbook of Chemidtry and Physics." 3 l s t ed., p. 2279, Cleveland, Ohio, Chemical Ruhher Puhlishiog C o . , 1949. Schiessler, R. W., et ul., "Synthesis and Propertie. of Hydrocarbons," API Project 42. Tilton, L. K., and Taylor, J . K., J . Rrsrarch .\-ut!. Bur. Staridards, 20, 419 (1938).
(1) Do**, 11. P.,
(2) (2)
(4)
(5) (6)
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 Department 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 Coinpound ;\dt,nosine .idenosine-.5'phosphoric acid Guanosine Cytidine I:ridine
" h
Wave Length. mpa 227 227 224 227 230
Aloles ( X 10'1 Moles, f X,10') of Riboside 3 63 0 97 3 00 4 10 4.l@
-ofPS!!odate -4dded 4.94 1.U8
4.94 4.94 4 94
Consumed 3 69
Ratio'
1 02 3 08 3 84 4 09
0.93 0 9Y
\Tart lcnath at xvhich disappearance of periodate was folloxed hloles of riboside to moles of periodate consumed.
@.!a
1
07
1.00
1093
V O L U M E 2 6 , NO. 6, J U N E 1 9 5 4 \-emon, S . I-,).The adenosine was a sample of material carefully purified in this laboratory. An aqueous solution of known concent,ration was prepared from each one of the ribosides. Ilistilled water which contains no appreciable amount of Iieriodate oxidizable impurities was used for preparing all solutions. Procedure. A Beckman 1Iodol DU spectrophotometer was usvl for iiieiieui ing absorbancies. Four quartz absorption cells with a 1.00-em. light path are filled with water and ahsorhance readings taken using one of tlie cells ( S o . 1 as a blank. Any absorbance differences for th? cells found in this way are later applied as corrections. Then ccllls 2 , 3, and 4 are emptied, dried, and filled in the following nixiner: Equal and known volumes of solution containing the oxiclizahle ssniple are added to cells 2 and 4 and the sitme volume of w:iter is put in cell 3. Similarly, equal and known volumes of 10-1.1f periodate solution-ea. 20 t'o 1 0 0 ~ oin excess-are :~tltle~l to cell5 3 and 4, while an equal volume of water is adt1e.l to crll 2 . The solutions in the cells are mixed and their ahsorhtuciw :ire measured a t 5- to 10-minute intervals against cell 1 as I~1:~nk.The absorbance of cell 4 subtracted from the sum of the :il)sorbniivire of cells 2 and 3 represents the decrease in ahsorlxince due to rtonsumption of periodate by the sample. When this :tlxorh:ince difference becomes constant in 60 to 90 niinut,es. the. i,eactioii is considered complete. This difference divided the al)sorh:incr of cell 3 at zero time is equal to the fraction of tlie known amount, of added periodate that is consumed in oxidizing the vicinal glycol groups. T h e absorllance of cell 3 is followed in order to correct for the slow changc in absorption which takes place in 10-4M solutions of nietaperiodat,e. This change presumably is due to changes i i ; teniprrnturp. pH. etc. ( 2 ) . The ribonucleo~idesare oxidized a t a rapid rate a t concentrations of 10-'111. K i t h substances which are oxidized a t incon-
veniently slow rates (hours or days for complete oxidation) in such concentrations-Le., ethylene glycol and a-methylglucoside-it is desirable t o alter the above procedure. I n such cases the reaction may be carried out a t concentrations about twentyfold higher in absorption cells with a 0.5-mni. path length. An alternative procedure, which also has proved useful, is to carry out the oxidation in much more concentrated solution, remove aliquots at dcisircd intervals, and dilute to a convenient volume for the at)s,irbanre readings. I n applying this spcctrophotometric method t o compounds whirh hnvi, t)clcTn eluted from a paper chromatogram, it is necessary to apply a correction for the periodate-oxidizable substances which arr rluted from the paper along with the desired material. This i-oiwction can be made readily by eluting a blank piece of 1 ) a p ~of r known area and determining spectrophotometrically the aiiio1unt of pciriodate consumed by- the eluate. A correction then may he applicd t o the amount of periodate consumed by the samplc based on the area of paper from which the sample was eluted. LITERATURE CITED (1) Adelberg, E. d.,. 1 ~ . 4 ~CHEY., . 25, 1553 (1953).
(2) Crouthamel, C. E., Hayes, A. 31., and Martin. D. S.,J . A m . C h e m . SOC..73, 82 (1951). (3) .Jackson, E. L., "Organic Reactions," Vol. 11, p. 341 Sew York, J o h n Wiley & Sons, 1944. RECEIVED for review December 23, 1953. Accepted Afarch 18, 1954. R e search supported in part by the United States Atomic Energy Commission i 3 based on the Ph.D. thesis of Jonathan S. Diuon, Washington r n i r e r s i t y , June 1933.
Determination of Adsorbed Moisture on Uranium and Uranium Oxide JAMES 0.HlBBlTS and DONALD ZUCKER Y - 1 2 Plant, Carbide and Carbon Chemicals Co., O a k Ridge, Tenn.
1,THOUC;H this niethotl was intended to determine only the older of magnitude of the per cent of moisture adsorbed O : I uranium anti uranium oxide (U30,) during treatment prior to wighirig. it was evaluated more precisely because of its general :tpidicability to other similar problems. Prohably t,he most important advantage of the Karl Fischer re:rgent is its ability t,o determine rapidly and accurately very sm:t11 quantities of waber. However, when the sample to he analyzed is insoluble in alcohol or the Karl Fischer reagent, or will react nit,h bhe reagent, as is the case with a number of iiiorgnnic salts and oxides ( 5 ) , a direct titration with Karl Fischer reagent would seem t,o be unsatisfactory. Recently ( 7 ) , t'he Karl Fischer titrat,ion has been employed for the determination of moisture in gases by passing a measured amount of gas through a known amount, of reagent. .1 modification of this technique was utilized to overcome the inherent disadvantages of direct titration of insoluble uranium and uranium oxide. The sample was placed in a quartz tuhe and heated, and the evolved moisture swept into a specially designed titration cell where it reacted with the reagent. The dead-stop cmi-point technique of Foulk and B a d e n ( 1 , ,3) was u d for di4wtiiig the en;l point, of the titration. REAGENTS
.lbsolute mrthanol. S o attempt \vas made t o desiccate or further purify the methanol. Karl Fischer reagent, prepared in the usual manner with 269 nil. of pyridine, 84.7 grams of iodine, 667 ml. of absolute met,hyl alcohol, and 64 grams of liquid sulfur dioxide. Standard water solution, prepared by the dilution of a known amount of lvnter with absolute methanol.
Sodium tartrate dihydrate, reagent grade. Barium chloride dihydrate, reagent grade. 1Iagnesium perchlorate, anhydrous. APPAR-ITU S
As only small amounts of water were t o be determined, the apparatus described has been used successfully t o keep contamination from atmospheric moisture t o a minimum prior to and during the titration. The initial pressure of the tank nitrogen, used as a sweep gas. was controlled by a low range (0 to 10 pounds per square inch, pressure regulator. Three drying ton-ers of anhydrous magnesium perchlorate were used for preliminary drying of the w e e p gas; remaining traces of moisture !%ereremoved by a dry ice--acet,one trap. Stopcocks on either side of the cold trap permitted fine control of the gas flow rate. The essential part of the heating tuhe was composed of 25-nini. quartz tubing, 65 em. in length. A standard taper 29/42 male joint was sealed t o one end of the tube t o serve as a sample port. An 8-mm. diameter side arm, 5 cm. from the sample port, allowed introduction of the sweep gas into the heating tube. A 15-cm. section of 8-mm. tubing was sealed to the exhaust end of the heating tube. -4lthough the dimensions of t,he quartz tube are not critical, the ground-glass joints must he located a t sufficient distances from the furnace to prevent volatilization of the joint lubricant when the tube is heated. The quartz tube was heated by a 12-inch tube furnace, whose temperature was controlled liy a variable autotransformer. Temperatures heloIv 300" C. were read from a thermometer plared in the tube: higher temperatures were indicated by a thermocouple placed outRide t,he tube in the heated zone. The position in the tube of platinum boats (3 X 3 / , X inches), which were w e d as sample containers, \vas adjusted with a steel rod which had a small hook a t one end for removing the sample boats.
