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Beauty or the Beast: Nitration of Phenol

One aftheabsolutelymcsaiesr enperimcnt~o he found in elmmenraryorgnn~rrhemstry ahuratorirs is the nitrntmt d

phenol uqthd ilut e aqueous nitriearrd. T he irnmrdiate result trfthr m i x ~ n gsa hlatk, itickvgoo that ndhrre$ perv~r stlg u

stirrmc r d s , 1asks. 2nd fingrrs. Hoacre r , upon h ~ l n gtram distil ld the najty gw r yivldr a decent crclp of n-nitrophenol

crvsta&. Thin-laver ehr oma to~ rsp hyf the in itial goo on Silica GelH with toluene as solvent reveals a complex spectrum of

yeilow, brown, o;ange, and bl&kspots or bands with plenty of material remaining at th e origin.

It isposs ihle ton it rat e phenol an dob tai n crystals of 2,4-dinitrophenol in high yield with nothing more repulsive than areddish-brown solution along the way. Th e key to this success is toeliminate the water presen t in the nitric acid as follows:

(1) To I.:, mL uf acet icanhydride in a 25.mL flask cooled in nn ce hath, add 2.0ml. of X O O HNCJ,dropwiat., krrping

thetemperature bdow R5'C.Stirnra~rlthesolution forsewral mlnutes.Allrheuaterpresrnt in th r nitric n c d iselimmated by rheaceticanhydride tufur m arrtir arid. (Caution! HS 0, nnd acme anhvdridr arr eorms iw; rmseoff 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 ad-dition. (Pheno l is also corrosive. See caut io n above.) The reaction at thi s temperature is rather slow,so removal of

the flask from the ice bath is recommended after all th e phenol has been added. Be ready to use the ice hath again if

the reaction tem perature exceeds50 'C.(3) When the reaction te mpera ture no longer rises, warm 8 mL of distilled water an d th e reaction flask on a steam

bath. Slowly add the water to t he solution with continued warming up t o 85-90 'C. Some oxides of nit rogen may be

given off during th e 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 filtrat ion and rinse with 7-10 mL of chilled 50% acetic acid.

The crys tals obtained can h e recrystallized from ethanol to yield 2,4-dinitrophenol with a melting point of 113-114 'C,identified by its IR spectrum a nd a mixed melting point of the same value.

Anearly worker in thisareaaddedphenoltotheaceticanhydridebefore nitrating, thus infactnitrating phenyl acetate

rather th an free phenol.' As a result he obtained yields ofo-

and p-nitrophenol, hut no mention of dinitro products. Wethank the Welch Foundation for their financial support of this research.

Thomas McCullough, CSC

Kassia KubenaSt. Edward's University

Austin. TX 78704

Volume 67 Number 9 September 1990 801