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Picric acid preparation, Laboratory & Industrial, Uses and Applications
Citation preview
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.