Preparation of Solid Derivatives by Differential Scanning Calorimetry
E. W. Crandall a n d Maxine Pennington Pinsburg State University Pinsburg, KS 66762
In the classical method of organic analysis the final step is the preparation and determination of the melting point of a solid derivative. Thermal methods have been used for vears ~ - ~ (1,2)to observe phase changes in materials. In 1964 O'Neill (3) modified t h e older DTA technique to give a n instrument in which the heat (enthalpy) change is directly proportional to the voltage differential between the sample and standard. This instrument is now commercially available a s the differential scanning calorimeter (DSC). In 1962 Chiu (41, using a modified DTA, reported the preparation of the P-nitro~henvlhvdrazoneof acetone and thepicrate of triethylamineby combining the readants in the sample p a n of the DTA and then observina the meltina ~ o i n t of t h e derivative along with phase transitions which t i m e d o u t to b e the hoiling points of t h e acetone and triethylamine. We have followed u p on the work of Chiu by preparing a number of solid derivatives of alcohols. amines. ohenols. aldehydes, ketones, and haloalkanes and by o b s e d n g the phase transitions using a differential scanning calorimeter. ~~
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A
The reactions were carried out in and all data obtained on a Perkin-Elmer DSC-1B differential scanning calorimeter. The instrument settings were as follows: range 8, heating rate 1O0C/min,chart range 10 and chart speed 10 mmlmin. Sample size varied from 0.5-2.0 mg. All scans were obtained by sealing the sample in one of two types of pans, one for volatile materials and one for nonvolatile materials. An empty pan and lid was used as the reference. The reagents chosen for this study were those which formed solid derivatives with short or no heating periods. The results are shown in the table. Aldehydes and Ketones
Summary of Derivatives and Comparison wlth Literature Melting Polnts -
DSC
Melting Point Aldehydes and Ketones benzaldehyde 2.4-DNP acetophanone 2,4DNP 4'rnethyiacetophenone 2.4-DNP benmphsnone 2.4-DNP benzaldehyde semicarbezone
+
+
+
+
+
benraldehyde methone AIwh0l~ 3-pentanal a-naphthylisocyanate dodecylalc~hol n-naphthyiisacyanate butanoi-1 a-naphthylisacyanate ethanol a-naphthylisocyanate Aminer di-n-propylamine a-naphthyiisocyanate n-propyiarnine a-naphthylisocymta piperidine + a-naphthylisocyanate Phenols phenol + pnitrobenzoyi chlwide eugenol + pnibobenzoyi chlwide reSOrCinOl + ~nibobenz~yl chloride Haloalkanes methyliodide thiourea pivic acid C-butylbrornide thiourea picric acid
+
Literature Melting Point (5)
510°K 510°K 52I0K 522'U 457'K 457°K 509'K 51I0K 506% 506OK (ifheated rapidly) 465'K 466'K
+
+
+
+
+
+ + + l-bromopernne + thiourea + picric acid
Tertlaryamlnas N,Ndimethylaniline+ methyliodide tribuiylarnine + methyliodide
2,4-Dinitrophenylhydrazones Two microdropsof the aldehydeor ketone were added to the sample pan from a capillary tube. A small amount of solid 2,4-dinitrophenylhydrazine was added and a lid sealed onto the pan. Semicarbazones One milliliter of aldehvde. . . 1 e- of semiearhazide hvdrochloride and 0.1 e of sodium acetate were mixed in a test tube andheated in a water forb min. Thc crystals which formed upm cmling were removed and sealed i n n sample pan without further purification. ~
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Methone Derivative Five drops of benzaldehyde, 0.2 g of methane and one drop of piperidine were dissolved in 2 ml of ethanol. The test tube was heated in a water bath for 5 min. The contents was poured onto a wateh glass and allowed to dry, after which the solid was sealed into a sample pan. Alcohols a-naphthylurethanes were prepared by mixing 1 g of t h alcohol ~ and 0.5 ml of
