Experiment # 7:

Preparation of Picric-

Acid

Date: 07, December 2010

Muhammad Usman

(2008-chem-02-B)

Water:

It is a non-hazardous compound.

Environmentally safe:

Water is an essential part of life. Life cannot be sustained without water.

Food & eatables contain some amount of water in them. It is a non-

hazardous compound.

IUPAC name Water

Oxidane

Other names

Hydrogen oxide

Dihydrogen monoxide

Hydrogen monoxide

Hydroxylic acid

Hydrogen hydroxide

R-718

Oxygen dihydride

Oxygen hydride

Oxane

Structure

Molecular formula H2O

Molar mass 18.0152833 gmol-1

Appearance

Density

1000 kg m-3

(liquid)

917 kg m-3

(solid)

Melting point 0 oC

Boiling point 99.98 oC

Acidity (Pka) 15.74

Basicity (Pkb) 15.74

Viscosity 0.001 Pa.S (20 oC)

3. Phenol:

Corrosive:

Phenol is a corrosive substance. It is a slightly acidic compound. Care should

be taken while handling phenol because it can damage to skin and clothing.

Toxic:

Phenol and its vapors are corrosive to the eyes, the skin, and the respiratory

tract. Inhalation of phenol vapor may cause lung problems. The substance

may cause harmful effects on the central nervous system and heart. The

kidneys may be affected as well. Exposure may result in death and the effects

may be delayed. Long-term or repeated exposure of the substance may have

harmful effects on the liver and kidneys." There is no evidence to believe that

phenol causes cancer in humans.

Properties of Phenol:

IUPAC name Hydroxybenzene

Other names Carbolic Acid, Benzenol, Phenylic Acid, Hydroxybenzene,

Phenic acid, Phenyl alcohol

Structure

Molecular formula C6H6O

Molar mass 94.11 gmol-1

Appearance

Density 1.07 g cm3

Melting point 314 k

Boiling point 455 k

Solubility in water 8.3 g/100 ml (20 oC)

Acidity (Pka) 9.95

Flash point 79 oC

1. Nitric acid:

Toxic:

Fumes from concentrated nitric acid are very damaging if inhaled

Corrosive:

Concentrated and moderately concentrated solutions are very corrosive

and can cause serious skin damage

Oxidant:

Contact with the eyes can cause serious long-term damage.

Properties of Nitric acid:

IUPAC Name Nitric acid

Other names

Oxoazinic acid

Aqua fortis

Salpetre acid

Spirit of nitre

Appearance Colorless liquid

Structure

Molecular formula HNO3

Molar mass 63.012 g mol-1

Density 1.5129 g cm-3

Melting point -42 oC

Boiling point 83 oC

Solubility in water Miscible

Acidity (Pka) -1.4

Flash point Non-flammable

Sulphuric acid:

Corrosive:

It is a strongly corrosive compound as it readily oxidizes anything.

Dangerous to Environment:

Although sulfuric acid is non-flammable, contact with metals in the event of a

spillage can lead to the liberation of hydrogen gas. The dispersal of acid aerosols

and gaseous sulfur dioxide is an additional hazard of fires involving sulfuric acid.

Very toxic:

Sulfuric acid is not considered toxic besides its obvious corrosive hazard, and the

main occupational risks are skin contact leading to burns and the inhalation of

aerosols. Exposure to aerosols at high concentrations leads to immediate and

severe irritation of the eyes, respiratory tract and mucous membranes.

Properties of sulfuric acid:

IUPAC name Sulfuric acid

Other names Oil of vitriol

Structure

Molecular formula H2SO4

Molar mass 98.06 g/gmol

Appearance

Density 1.84 g/cm3 (liquid)

Melting point 10 oC

Boiling point 337 oC

Solubility in water Miscible

Acidity (Pka) -3

Viscosity 26.7 cP (20 oC)

Flash point Non- flammable

2. Ethanol:

Harmful: Pure Ethanol will irritate the skin and eyes. Nausea, vomiting and intoxication

are symptoms of ingestion. Long term use by ingestion can result in serious liver

damage. Death from Ethyl alcohol consumption is possible when blood alcohol

level reaches 0.4%.

A blood level of 0.5% or more is commonly fatal. Levels of even less than 0.1%

can cause intoxication, with unconsciousness often occurring at 0.3–0.4%

Highly flammable: It has a flash point of 13

oC. It can readily catch fire. So care should be taken

while handling it because its combustion products include Acetaldehyde which

is a strongly carcinogenic substance. However, ethanol itself is not cancer

causing.

Properties of Ethanol:

IUPAC Name Ethanol

Other names

Absolute alcohol

Drinking alcohol

Ethyl alcohol

Ethyl hydrate

Grain alcohol

Hydroxy-Ethane

Appearance Colorless liquid

Structure

Molecular formula C2H6O

Molar mass 46.07 g mol-1

Density 0.789 g cm-3

Melting point -114.3 oC

Boiling point 78.4 oC

Solubility in water Miscible

Acidity (Pka) 15.9

Flash point 13 oC

Auto-ignition temperature 422 oC

Preparation of picric acid

Chemicals Required:

1. C2H5OH 2. HNO3 (concentrated)

3. H2SO4 (Concentrated)

4. Distilled water

5. Phenol

Apparatus:

1. Pipette 2. Stirring rod

3. Filter paper 4. Funnel

5. Ice bath 6. Beaker

Chemical Reaction:

C6H5OH(s) + H2SO4 (l) HO-C6H4-SO3H + HNO3 (aq) C6H3N3O7

Procedure:

1. 25grams of powdered phenol are added to a 250ml beaker containing 31.25ml (57.81g) of

concentrated sulfuric acid.

2. The mixture is stirred and than heated on a hotplate at 100oC for 30 minutes until it becomes

dark colored, indicating the formation of phenol-4-sulphonic acid.

3. This is then chilled to -5oC on a water bath with salt added, becoming a cold viscous syrup, to

which 47ml of chilled (-5oC) nitric acid are added inside a fume cupboard, making sure that the

mixture is not allowed to warm up prior to the addition of the acid. Within a few minutes

vigorous reaction occur producing large amounts of nitrogen dioxide, a red colored

(poisonous!) gas.

4. The reaction is allowed to subside and than the mixture (which has now become a thin,

orange/yellow liquid) is heated on a water bath for one and a half hours, with occasional

shaking.

5. When the heating is complete the mixture is allowed to cool down and 313ml of cold water are

added, causing the Picric Acid to crystallize out of the mixture. The mixture is cooled to 5oC so

as to precipitate most of the remaining Picric acid, and than is quickly filtered and washed with

1200mL of cold distilled water so as to remove any traces of the nitration acids.

6. The filtrate appears as the fine yellowish mass of crystals seen to the left. Yield is

approximately 40grams for the 25 grams of phenol that was started out with. These crystals are

high purity and have all of the properties attributed to reagent grade Picric Acid. However, they

can be purified.

7. Making use of Phenol's high water solubility, and the higher solubility of dinitro and mononitro-

Phenol, the Picric Acid can be purified to near analytical grade by re-crystallization from a

solvent mixture of 1 volume ethanol and 2 volumes water, roughly 9ml of solvent being required

per gram of Picric Acid

8. The crystals are than removed by vacuum filtering, are vacuum dried in a dissector, and form into

a nearly yellow mass of mp 123oC.

It is advisable to store Picric Acid wet with at least 30% water and in rubber stoppered flasks

Uses of Picric acid:

1. The largest use of picric acid has been in Explosives.

2. In microscopy, picric acid is a reagent for staining samples. It has found some use in organic

chemistry for the preparation of crystalline salts of organic bases (Picrates) for the purpose of

identification and characterization.

3. In metallurgy a picric acid etch has been commonly used in optical metallography to reveal

prior austenite grain boundaries in ferritic steels.

4. Bouin's picro-formol is a preservative solution used for biological specimens.

5. Workplace drug testing utilizes picric acid for the Jaffe Reaction to test for creatinine. It

forms a colored complex that can be measured using spectroscopy.

6. Much less commonly, wet picric acid has been used as a skin dye or temporary branding

agent. It reacts with proteins in the skin to give a dark brown color that may last as long as a

month.

7. In the early 20th century, picric acid was stocked in pharmacies as an antiseptic and as a

treatment for burns, malaria and smallpox.