urbaf2

NITRO DERIVATIVES OF PHENOL 491

Heat of nitration. The heat of conversion of phenol into picric acid has been

calculated on the basis of the above data (see diagram on. p. 261):

phenol - o- and p- nitrophenol +35.0 kcal/mole

o- and p- nitrophenol - 2,4-dinitrophenol +24.5 keel/mole

2,4-dinitrophenol - picric acid + 12.9 keel /mole

+72.4 kcal/mole

Heat of explosion - see below, under explosive properties.

CHEMICAL PROPERTIES

An outstanding feature of picric acid is its acidic character. It readily forms

picrates (they are dealt with in a special chapter, p. 525) and esters, which are phenol

ethers, e.g. trinitroanisole (p. 545), trinitrophinetole (p. 548).

Like other polynitroaromatic compounds, picric acid readily forms addition

products with aromatic hydrocarbons. This behaviour is especially pronounced

in picric acid. Addition compounds with phenols, aromatic ketones, acids and

even with nitro compounds are also known.
Here are some of the addition compounds formed by picric acid combined with

other substances in molecular proportion of 1: 1:

Second component Melting points, °C

Anthracene ca. 141 (non uniform melting)

Benzene 84

Fluorene a4

Naphthalene^150

Phenol^85

Resorcinol^100

Pyrocatechol^124

Guaiacol 88.6

o- Cresol 89.8

p -Cresol ca. 65.6 (non uniform melting)

Thymol 96.8

β -Naphthol 145.8

Triphenylcarbinol 138.5

Acetophenone ca. 50 (non uniform melting)

Benzophenone 27 (readily dissociates)

Cinnamic acid 106.5

With m- cresol, picric acid forms a compound (m. p. 61.6°C) containing the

two constituents in the mol. proportions of 1: 2. With salicylic aldehyde it forms two

non-uniformly melting compounds in the proportions of 1: 1 (m. p. - 55°C) and

1: 2 (m. p. - 35°C). With m- hydroxybenzoic aldehyde, picric acid forms a series

of compounds containing the constituents in proportions from 1: 1 to 1: 5, dissoci-
ating at 90°C on melting.

Jefremov [53] was able to identify the following compounds in molecular pro-

portion 1: 1 by means of thermal analysis: