David Yung, Larry Whitehouse, and Edmund 10 College of Pharmacy Dalhousie University Halifax, N.S. Canada
I
I
Identifying Phenols using N-Methylpiperazine and N-Phenylpiperazine
The salts of N-methylpiperazine and Nphenylpiperazine have been shown to he useful derivatives in identification of carboxylic acids.' One distinct advantage of these monosubstituted piperazinium salts over the other derivatives of carboxylic acids is their ease of formation. The purpose of this work is to determine if N-methylpiperazinium and N-phenylpiperazinium salts can serve as useful derivatives in characterization of another class of acidic compounds namely, phenols. Experimental N-Methylpipermine, N-phenylpiperazine, and the phenols employed in this study were obtained through commercial sources and were used without further purification. The melting points were determined using a Thomas Hoover melting point spparetus
nnrl nre ~~nr.nrmot,eA. ..~~...~.
The salts were prepared in the folloainfi munncr. The phenol (0.3-1E) WRR ~ ~ S S O Iit, VC a minimum J nn~ounlof nnhydroui rther or any other suitable solvent such as dry benzene, acetone, and absolute ethanol. To this solution was added dropwise and with stirring N-methylpiperaiine or N-phenylpiperaeine (0.5-1 ml). If the desired salt precipitated immediately the mixture was allowed t o stir for 5 min at room temperature and the salt wes collected by filtration. If there was no immediste salt formation the etheral solution was refluxed on a steam bath for 10 min. After cooling the solution wes placed in a refrigeretar until the The crude product was washed thoroughly salt precipitated. with anhydrous ether and then recrystallized from a. mixture of
with N-methylpiperazine. For these reasons, Nmethylpiperazine does not appear to be a suitable reagent for derivative formation in identifying phenols. The fact that the phenol-N-phenylpiperazinium salts are quickly and easily prepared and readily purified suggests that N-phenylpiperazine can be used as a reagent for the preparation of derivatives of phenols. In most instances, the salt formation occurred almost instantaneously and this is definitely an advantage over some of the other traditional phenol derivatives. The majority of phenols studied in this work are soluble in ether, benzene, acetone, and absolute ethanol. In a series of experiments designed to determine the best solvent, it was shown that the yields were consistently higher when anhydrous ether was used. For example, the percent yields of N-phenylpiperaziniurn salt of phromophenol in anhydrous ether, absolute ethanol, acetone, and dry henzene were found to be 63, 21, 9, and 21, respectively. In Table 2 are listed the seven N-methylpiperazinium and N-phenylpiperazinium salts whose results of eleTable 2. N-Phenylpiperazinium and N-Methylpiperazinium Salts with Unsatisfactory Elemental Analyses
acetone and n-hexane.
Results and Discussion
As indicated in Table 1, 45 of the 88 phenols studied yielded crystalline N-phenylpiperazinium salts, whereas only 10 phenols formed salts with N-methylpiperazine. Phenols that failed to produce a satisfactory derivative with N-phenylpiperazine also gave negative results DUFF,J. G., YUNG,D. K., BRENNER, R. J., WILSON, B. J., Racz, W. J., J. CHEM.EDUC.,46,388 (1969).
AND
474
/
Journal o f Cherni'cal Education
Salts
N-Pheny1piperaaine.p.p'biphenol N-Phenylpiperaaine. 2.6-dihromo-4-nitrophenol N-PhenyIpiperarine.2 naphthol N-Phenylpiperarine.1.4naphthalenedid N-hletl>ylpiperazine. 2.5-di0111"10,?11."01 N-Methylpiperaaine.2.4dinitropl~enol N-Methylpi~eraeine.2.4.0triohloroohenol
Melting Point, 'C.
137-139
C% H% Calo d. Calc d. Found Found 75.26 7.50 41.85 73.78 7.20 3.73
181-183 46.90 100.5-102.5 78.40 77.66 151-153 74.50 70.03 50.21 91-92 48.05 210.5-211.5 40.46 48.70 145-148 44.40 43.83
4.51 7.24 7.41 6.87 6.30 0.13 4.92 5.08 4.30 5.08 4.60
Table 1.
Physical Data of N-Phenylpiperazinium and N-Methylpiperoziniurn Salts of Some Phenolsa
... ... ... ... ... ... Melting point range too wide ... ... ...
No derivative formation
27
121-iis
NO dC;iustiue format&
No derivative lormation No derivative formation No derivative formation
...
... ...
...
...
...
...
...
oil
No derivative formation N o derivative formation
90.5-92 oil 80 62.0-62.5 54 46.5-47 No derivative formation
