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p-DCB is produced by chlorination of benzene using ferric chloride as a catalyst: . C 6 H 6 + 2 Cl 2 → C 6 H 4 Cl 2 + 2 HCl. The chief impurity is the 1,2 isomer.The compound can be purified by fractional crystallization, taking advantage of its relatively high melting point of 53.5 °C; the isomeric dichlorobenzenes and chlorobenzene melt well below room temperature.
Boiling point (°C) K b (°C⋅kg/mol) Freezing point (°C) K f (°C⋅kg/mol) Data source; Aniline: 184.3 3.69 –5.96 –5.87 K b & K f [1] Lauric acid: 298.9 44 ...
There are three distinct chemical compounds which are dichlorobenzenes: . 1,2-Dichlorobenzene or ortho-dichlorobenzene;; 1,3-Dichlorobenzene or meta-dichlorobenzene;; 1,4-Dichlorobenzene or para-dichlorobenzene.
Freezing is a phase transition in which a liquid turns into a solid when its temperature is lowered below its freezing point. [ 1 ] [ 2 ] For most substances, the melting and freezing points are the same temperature; however, certain substances possess differing solid-liquid transition temperatures.
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A bath of ice and water will maintain a temperature 0 °C, since the melting point of water is 0 °C. However, adding a salt such as sodium chloride will lower the temperature through the property of freezing-point depression. Although the exact temperature can be hard to control, the weight ratio of salt to ice influences the temperature:
Older mothballs consisted primarily of naphthalene, but due to naphthalene's flammability, many modern mothball formulations instead use 1,4-dichlorobenzene.The latter formulation may be somewhat less flammable, although both chemicals have the same NFPA 704 rating for flammability.
The phenomenon of freezing-point depression has many practical uses. The radiator fluid in an automobile is a mixture of water and ethylene glycol. The freezing-point depression prevents radiators from freezing in winter. Road salting takes advantage of this effect to lower the freezing point of the ice it is placed on.