A n Improved Methoxyl Apparatus A. J. BAILEY, University of Washington, Seattle, Wash.
C
OMMON methods of methoxyl assay employ a cumber-
some and complex apparatus. The standard method of the Technical Association of the Pulp and Paper Industry (3) uses three separate pieces of apparatus for maintaining temperature in t h e assay system, while t h a t of Peniston and Hibbert ( 2 ) employs four separate units; other methods require generally similar equipment. T h e proposed apparatus represents a simplification in apparatus with greatly improved operating characteristics.
Apparatus A diagram of the apparatus is shown in Figure 1. The apparatus was patterned, in part, after the standard T. A. P. P. I. apparatus (S),but embodies an internal electrical heater rather than an external heating unit, and the absorption system is simplified. Greatly simplified control is one of the major advantages. OPERATION.Best results were obtained by heating the glycerol bath (I,Figure 1) on a small adjustable, thermostatically controlled hot plate (Central Scientific Co., Catalog No. 16,627), which maintained the bath a t 130' C. with almost no change for
FIGURE1
METHOXYLAPPARATUS
hours on end. The heater immersed in the jacket was connected to the alternating current line through a fixed resistance of such size as to maintain the jacket temperature a t 55". With the trap and absorption tubes filled, the sample was introduced, and the apparatus was closed and lowered into the glycerol bath. Introduction of a slow stream of carbon dioxide completed the necessary adjustments. This apparatus was in full-day operation for several weeks at a time; once adjusted, virtually no further adjustments were required and supervision was necessary only at hourly intervals to change absorption tubes and scrubbing liquid and to introduce a new sample and, if necessary, new hydriodic acid and phenol. It was found desirable to add samples in a small glass boat and to use an antibump tube as shown. Three or four samples were hydrolyzed with 15 ml. of hydriodic acid (specific gravity 1.7) before the flask was replaced with a new flask and fresh reagent. The addition of phenol was not necessary, but contributed to a shorter time and smoother reaction. As Clark ( I ) and Peniston and Hibbert (2) noted, the apparatus and reagents must be heated before use to free the system completely of methoxyl. All grades of phenol used in this laboratory have given positive tests for methoxyl. A convenient method of testing for completion of removal of methoxyl is to use an absorption tube containing alcoholic silver nitrate. In addition to the causes of error recorded by Peniston and Hibbert necessitating a blank determination, a prolific source of blank correction was found t o be the instability of potassium iodide solution. Even short standing caused a faintly yellow solution (formation of free iodine) and consequent large blank correction.
Variations in Method
Drawn]. to scale
This apparatus was used with equal success in the Zeisel ( 5 ) )Viebock and Schwappach (C), and Peniston and Hibbert ( 2 ) methods and gave an accuracy identical t o t h a t obtained by the older apparatus. It should give identical accuracy in Clark's (1) and similar methods. I n the Peniston and Hibbert method the addition of phenol t o the flask was not essential and carbon dioxide was used directly from a tank. A phosphorus suspension and a 5 per cent cadmium sulfate-5 per cent sodium thiosulfate solution gave identical results as a scrubbing medium. With t h e size of sample ordinarily used in the Zeisel method, the silver nitrate absorbing solution and subsequent gravimetric determination gave lower accuracy than the bromine-potassium acetate-glacial acetic acid absorbing solution ( 2 ) and subsequent volumetric determination of the iodine. T h e latter method possesses great advantages in simplified procedure, high inherent accuracy, freedom from interference, rapidity, and ability t o use extremely small samples. This apparatus has been in successful use in the author's laboratory for several years in the analysis of methoxy phenols and lignin preparations, and has been used by Irwin A. Pearl of this laboratory in recent months with similar success and satisfaction. The method employing the volumetric determination of iodine, substantially as described b y Peniston and Hibbert but modified as above, has been found to be most accurate and convenient. It consistently gave values that varied less than 0.1 per cent from the theoretical with 3to 7-mg. samples of vanillin; in general, accuracy was similar t o that reported b y Peniston and Hibbert.
A , 7 m m . ; B , 2 2 m m . ; C, 8 mm.; D , 5 mm.; and E , 10 mm. in outside diameter. F , electrical leads, approximately 4 feet of No. 26 Nichrome wire; G, water jacket a t 55" C.; H , CO1 inlet; I , glycerol bath a t 130'. Over-all length of water jacket was 60 om., outside diameter 38 mm.; a thermometer was suspended inside. Glycerol bath was maintained a t constant temperature by thermostatically controlled heater. I
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Literature Cited (1)
Clark, E. P., J. Assoc. Oficial Agr. Chem.,15, 136-40 (1932).
Q.P., and Hibbert, H., Paper Trade J.,109,46-8 (Oot. 26, 1939). (3) Technical Assoc. of Pulp and Paper Ind., "Methoxyl Groups in Wood", T.A . P. P. I . Standard TZm (1934). (4) Viebock, F.. and Schwappach, A., BIT., 63,2818-23 (1930). (5) Zeisel, S.,Monatsh., 6,989 (1885); 7,406 (1886). ( 2 ) Peniston,
CONTRIBUTION from the Department of Chemistry and Chemical Engineering and Lignin and Cellulose Research Laboratories.
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