INDUSTRIAL AND ENGINEERING CHEMISTRY
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Vol. 15, No. 9
Determination of Beta-Naphthol in Alpha-Naphthol and of Alpha-Naphthol in Beta-Naphthol1 By John Prochazka CENTRAL DYESTUFF & CHEMICAL Co., NEWARK, ru'. J.
I
N 1897 Liebman2 published a method of determining
small quantities of a-naphthol in @-naphthol, founded on the greater affinityof trheformer for diazo compounds. This was an improvement on an older method described by the same investigator in the same article, founded on the color imparted to the precipitate formed with ferric chloride and naphthol in alcoholic solution. About the same time the author employed the same principles as Liebman in a method devised by himself and published later.3 To his knowledge no method of determining the percentage of a small quantity of @-naphtholin a-naphthol, except the one described by Fierzj4has been published. A number of years ago it was found desirable to work out a method for the determination of @-naphthol in a-naphthol, in connection with the manufacture of Pure Orange I made from pure a-naphthol, the use of which as a food color was authorized by law. The first thought was to make use of the well-known insolubility of @-naphthol azo compound in caustic soda as opposed to the solubility of the a-naphthol compounds. The chief objection to this method is the formation of a small quantity of what is presumably an ortho azo compound of a-naphthol, which also is insoluble in caustic soda. Another difficulty is the retention of a part of the a-naphthol compound in the insoluble @-naphthol compound. Experimqnts were made with diazobenzene, diazoxylene, p-nitrodiazobenzene, and p-nitrodiazoxylene. Further experiments were made based on the selective a f h i t y of diazo compounds for a-naphthol. Contrary to F i e r ~ . diazobenzene .~ combines, although slowly, with @naphthol in acid-especially, acetate and acetic solution-so that any method based on the supposed inability of @-naphthol to combine must give erroneous results. Moreover, the method described is cumbersome and difficult of execution. The same is true of a method employed in this laboratory. a-Xaphthol was dissolved in grain alcohol, and combined with 50 per cent of the theoretical p-nitrodiazobenzene, the precipitate was filtered off hot and washed with hot water, and the filtrate extracted with benzene, the benzene extract evaporated, and the recovered naphthol treated the same as the original sample until the point was reached where part of the @-naphthol was coupled. The @-naphthol compound was separated from the a-naphthol in hot caustic solution, and the para red weighed, examined as to purity with the sulfuric acid color test, thus obtaining an approximate idea of the percentage of the @-naphthol. PROCEDURE From this method the following very simple procedure was developed : Diesolve 0.36 gram a-naphthol in 30 to 40 cc. grain alcohol. Cool off to below 5" C. Add gradually a solution of p-nitrodiazobenzene, of which 100 cc. are equivalent to 1 gram of nitrite. This solution may be prepared accord1 Presented before the Division of Dye Chemistry a t the 65th Meeting of the American Chemical Society, New Haven, Conn., April 2 t o 7, 1923. * J . SOC.Chem. I n d . , 16, 290 (1897). 8 I b i d . , 16, 894 (1897).
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Farben Chemie, 1920, 296.
ing to known methods. It should contain only a very slight excess of nitrous acid, and a not too large excess of hydrochloric acid (30 to 50 per cent of theory). If the a-naphthol is 100 per cent, 17.25 cc. diazo solution would be needed to convert it to the azo compound. If the sample is supposed to contain 10 per cent @-naphthol, add about 85 per cent of the theoretic quantity-viz., 14.6 cc. of the diazo solutionstirring carefully and keeping cold. The color begins to separate a t once. It is well to wait 20 to 30 minutes, as the reaction takes time for completion. Then spot on a piece of white filter paper. If the reaction is not complete a spot of dilute caustic soda running into the first spot will produce a blue line if there is unchanged a-naphthol present. If the a-naphthol falls short of the 85 per cent diazo, the @naphthol will combine and the mixture of the a- and @-naphthol will produce a gray line with the caustic, or the @-naphthol alone will give a red line, this red line sometimes appearing outside of the gray line. If all the diazo solution has been absorbed, the caustic soda will produce only a faint color, owing to the little azo compound dissolved in the solvent. If the @-naphthol does not show, continue adding the diazo until the para red due to the @-naphtholpresent begins to show in the spot test RS described. If the quantity of diazo solution added is 16 cc., 16:17.25 rebresents the purity of the a-naphthol-viz,, 92 to 93 per cent. PROCEDURE FOR DETERMINATION O F a- I N fl-N.4PHTHOL Dissolve 1.44 grams P-naphthol in 50 cc. grain alcoliol and add 3 cc. p-nitrodiazobeneene and 0.03 gram nitrite. If the percentage is less than 0.5, all the a, and some fl will be precipitated as p-nitroazobenzene compound. Let stand half an hour, then dilute with 60 cc. boiling water, filter hot through a suitable filter, and wash the precipitate with hot water. All the 8-naphthol not combined passes into the filtrate, with some impure azo compound of the or-naphthol. The precipitate is washed off the filter, boiled with 50 cc. hot water containing 1 cc. 25 per cent caustic soda, filtered hot, diluted to 100 cc., and compared with a standardized solution of p-nitroazobenzene a-naphthol. This solution is prepared as follom7s: 0.1 gram of the azo compound is dissolved in 25 cc. warm grain alcohol containing 1 cc. 25 per cent caustic soda and diluted to 50 cc. with hot water. The alcoholic Gltrate is also made alkaline with caustic soda and compared with the standard. It is generally not as pure blue as the standard, but is included in the calculation. CALcuLATIox-If the standard is diluted about thirty times to match its color with the solution in question, with strips of filtering paper dipped in, it would mean that 30 x 500, or 1500 cc. of it contain 0.1 gram color, and as there are only 100 cc. these would contain 0.1/15 = 0.0066 gram. 1.44 grams naphthol would yield 2.93 grams azo compound; hence, the percentage of a-naphthol would be 0.0066/2.93 = 0.23 per cent. Figured to simplest form, diyiding 6.9 by dilution factor-30 in this case-gives 0.23 per cent. If more diazo solution is added, it is impossible to extract all the alpha compound from the para red. If, however, more a-naphthol is present, more diazo should, and can, be added. The chief objection to Liebman's method2is the extremely
September, 1923
INDUSTRIAL A N D ENGINEERING CHEMISTRY
fugitive character of the blue color. In an experiment made in this laboratory according to his direction, the color faded after 20 minutes. The coloration obtained in the method here described is also fugitive, but holds out conaiderably longer. As the standard solution is not very
945
stable, it was replaced by a solution of Diamine Blue 2B (benzidine tetrazotized and coupled with H acid in soda solution), the strength being adjusted to the freshly prepared standard. I n diluting the standard it is well to add 1 cc. caustic to every 50 cc. of pure distilled water used. e.
Bath Temperatures of Viscometers of t h e Saybolt Type’’z By Winslow H. Herschel BUREAUOB
STANDARDS, W A S H I N G T O N ,
D.
c.
V
TSCOSITY a t A given Standard temperatures should be adopted for the Saybolt viscomat 2120 F.7 it was contemperature is a eter bath in order to get reproducible results. cluded that mechanical Times of flow thus obtained cannot be used to calculate absolute stirring should be used in definite physical conoiscosities at the nominal temperature of test. unless allowance is order to get a SUffiCientlY stant of a liquid, and a vismade for the difference between the nominal temperature of test uniform temperature of Oil cometer may be judged and the average temperature of oil in the outlet tube during the run. in the O i l tube before witheither as an instrument to The variation of temperature in the oil tube during the run may drawing the Oil tube therdetermine true viscosity a t be observed, in the U and F viscometer, from readings of a thermometer and starting the a known temperature, Or as mometer kept in the oil tube during the run, and the average oil test. When tests are made a n instrument to obtain tube temperature may be used in calculating correction factors a t 210’ the determinaSome measure 01 indication for obtaining the absolute viscosity at the nominal temperature of test. tion of a Proper method of of viscosity under specified conditions. In thelatter case operation is further comthe important consideration plicated by the “cooling is whether results of different laboratories agree, but it has error,”5 and mainly tests a t the standard temperature of been found very difficult, if not impossible, to obtain adequate 100’ F. will be considered here. agreement unless instruments are so standardized as to be THEU AND F VISCOMETER^ suitable for obtaining true viscosity a t a known t,emperature. Where the viscometer tube is almost completely submerged In designing the u and F viscometer shown in Fig. 1, in a constant temperature bath, and there is little or no doubt the author had in mind an instrument which might be used that the liquid in the capillary or outlet tube is a t the same to measure absolute viscosity, and which would also be in temperature as the bath during the entire period of test, agreement with other instruments of the Saybolt type when there is no question in regard to the proper bath temperature. used to measure Saybolt viscosity in seconds. The essential There is only a question of its constancy. When, however, dimensions have therefore been chosen to conform with the a part of the instrument containing the oil under test pro- saybolt i n S t ~ ~ m e n t . ’ I n Preliminary tests8 it was found that the temperature jects above the level of the bath, as in the Saybolt and Barbey viscometers, a distinction must be made between in the Oil tube could be kept constant during the run by a the actual and nominal temperatures of test, the former Proper choice of bath temperatures, but, as was found later, being the average temperature in the outlet tube during this method of selecting the bath temperature is not of the timed interval. The difference between the actual general application, as it is not Possible with very heavy To keep the average and nominal temperature of test will be called the temperature Oils at 100” F. nor in tests a t 210” F. error, and there is a question as to what is the proper bath temperature Of the oil in the oil tube at the nominal temperatemperature to reduce this temperature error to a minimum, ture of test necessitates a variation of bath temperature which or what correction to apply to the observed viscosity. cannot be readily attained with thermostatically controlled According to the usual directions for operating the Saybolt baths. It therefore Seems Preferable to define Saybolt viscometer,3 “The bath shall be held constant within viscosity as the time of flow in seconds when the bath is 0.250 F. (0.140 c.)a t such a temperature as w-i;ill maintain kept constant a t a predetermined temperature, a standard the desired temperature in the standard oil tube.” This bath temperature to be agreed upon for each nominal temmight be taken to mean only that the reading of the oil tube perature Of test. Correction factors must then be used to thermometer shall be kept constant until the run is started, determine absolute viscosity, when desired, from readings since it is usual practice to withdraw the thermometer of Saybolt viscosity. It is desirable, for reasons which will be discussed later, before starting the run. I n view of this uncertainty and the increased accuracy now demanded in technical viscometry,4 to observe the variation in the temperature of the oil in the further standardization of bath temperatures appears de- oil tube during the run, as an aid in obtaining correction sirable, and this paper is offered as an aid in this direction. factors, and it is believed that these observations are also At the Pittsburgh meeting of the AMERICAN CHEMICAL SO- Of Value aS an indication whether O r not the oil under test CIETY a paper was presented before the Petroleum Section by has been sufficiently stirred and is of sufficiently uniform Klopsteg and Stannard on “Some Factors Affecting the Ac- temperature throughout before starting the run. To obcuracy of Saybolt Viscosity Measurement and Their Control.” tain these readings it is necessary to leave the thermometer From tests made at 2100 F. with the bath temperature in the oil tube during the run, and in the U and F instrument the diameter of the oil tube has consequently been enlarged 1 Presented before the Division of Petroleum Chemistry a t the 65th F a ,
Meeting of t h e American Chemical Society, New Haven, Conn., April 2 t o
7,1923.
* Published
b y permission of the Director, U. S. Bureau of Standards. Bur. M i n e s , Tech. Paper SaS, 37 (1923). 6 Delbridge, Proc. A m . Soc. Testing Materials, 21, 1100 (1921); “Lubrication,” T h e Texas Co , February, 1922, p. 22. 8
Herschel, Bur. Standards, Tech. Paper 210, 231 (1922). U and F means Universal and Furol, and the name was chosen because this instrument, by changing the outlet tube, may be used either as a Saybolt Universal or Saybolt Furol viscometer. 7 Am. SOC. Testing Materials, Standards, 1921, 703. 8 Herschel, Bur. Standards, Tech. Paper 210, 235 (1922) 6
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