Beauty or the Beast: Nitration of Phenol One aftheabsolutely mcsaiesr enperimcnt~to he found in elmmenraryorgnn~rrhemstrylahuratorirs is the nitrntmt d phenol uqthdilute aqueous nitriearrd. The irnmrdiate result trfthr mix~ngisa hlatk, itickvgoo that ndhrre$perv~rstlgt u stirrmc r d s , 11asks.2nd fingrrs. Hoacrer, upon h ~ l n gstram distilld the najty gwr yivldr a decent crclp of n-nitrophenol crvsta&. Thin-laver ehromato~rsphyof the initial goo on Silica Gel H with toluene as solvent reveals a complex spectrum of yeilow, brown, o;ange, and bl&kspots or bands with plenty of material remaining a t the origin. It ispossihle tonitrate phenol andobtain crystals of 2,4-dinitrophenol in high yield with nothing more repulsive than a reddish-brown solution along the way. The key to this success is toeliminate the water present in the nitric acid as follows: (1) To I.:, mLuf aceticanhydride in a 25.mL flask cooled in nn ice hath, add 2.0 ml. of X O O HNCJ,dropwiat., krrping thetemperature bdow R5'C.Stirnra~rlthesolution forsewral mlnutes.Allrheuaterpresrnt in thr nitric n c d is elimmated by rheaceticanhydride tufurm arrtir arid. (Caution! H S 0 , n n d acme anhvdridr arr eormsiw; rmse off any spills or skin contact with plenty of water) (2) Add 1.OmLof 9O%phenoldropwise to theacid solution, again keepingthe temperature below 35 'C during the addition. (Phenol is also corrosive. See caution above.) The reaction a t this temperature is rather slow, so removal of the flask from the ice bath is recommended after all the phenol has been added. Be ready to use the ice hath again if the reaction temperature exceeds 50 'C. (3) When the reaction temperature no longer rises, warm 8 mL of distilled water and the reaction flask on a steam bath. Slowly add the water to the solution with continued warming up t o 85-90 'C. Some oxides of nitrogen may be given off during the heating so use of a hood is recommended. (4) Set the clear reddish solution aside to cool slowly. A fine crop of yellow crystals should form even above room temperature. (5) Collect the crystals by vacuum filtration and rinse with 7-10 mL of chilled 50% acetic acid. The crystals obtained can he recrystallized from ethanol to yield 2,4-dinitrophenol with a melting point of 113-114 'C, identified by its IR spectrum and a mixed melting point of the same value. Anearly worker in thisareaaddedphenoltotheaceticanhydride before nitrating, thus infactnitratingphenyl acetate rather than free phenol.' As a result he obtained yields of o- and p-nitrophenol, hut no mention of dinitro products. We thank the Welch Foundation for their financial support of this research.
Thomas McCullough, CSC Kassia Kubena St. Edward's University Austin. TX 78704
Volume 67
Number 9
September 1990
801
