Medicinal gases in inorganic chemistry, Summaries of Pharmaceutical Analysis

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MEDICINAL GASES

By

Y Nagarjuna Reddy

Asst professor

M Pharm(Pharmaceutical Analysis and Quality Assurance )

Introduction

Def:

These are the inorganic substances meant for administration through nasal cavity. They may be given to patient for diagnosis, therapy and to produce anaesthesia.

❖ Oxygen ❖ Carbon dioxide ❖ Nitrous oxide ❖ Nitrogen ❖ Helium

Oxygen

Physical and Chemical Properties;

● Oxygen is a colourless, tasteless and odourless gas. ● It is slighty heavier than air ● It is sparingly soluble in water, but is freely soluble in alcohol ● the molecular form of oxygen (O₂) dissociates into the atomic form (O) completely. The atomic form of oxygen is much more active than the molecular form. Oxygen combines with most metals directly.

Official Tests for Identity

● 1. Oxygen causes a glowing splinter to burn brightly. ● 2. Oxygen is absorbed when it is shaken with alkaline pyrogallol solution. The solution turns dark brown. ● 3. When oxygen is mixed with an equal volume of nitric oxide, red fumes are produced (distinction from nitrous oxide).

Oxygen

Standard:

Oxygen contains not less than 99 percent v/v

Assay:

This assay is based on the fact that

certain substances such as pyrogallol in

alkaline solution absorb oxygen completely

and the volume of other gases such as

nitrogen, argon.or hydrogen can be measured

easily.

Carbon Dioxide

Carbon dioxide is present in the atmosphere to the extent of about 0.03%. It is a product of combustion, respiration and fermentation reactions.

Preparation

1. It may be prepared by heating alkali carbonates and bicarbonates. 2NaHCO3 = Na₂CO3 + CO₂+ H₂O
2. It may also be prepared by the action of acids on carbonates or bicarbonates. Na₂CO3 + H₂SO4 = Na₂SO4 + CO₂ + H₂O Carbon dioxide is also formed from the products of combustion of coke, from fermentation and during the manufacture of lime by burning limestone in lime kilns

Carbon Dioxide

Physical and Chemical Properties

● Carbon dioxide is a colourless and odourless gas. ● It is freely soluble in water and the aqueous solution ● It is about one and a half times heavier than air. ● Carbon dioxide does not support combustion. A burning splinter is extinguished when it is introduced into a jar containing carbon dioxide. ● It dissolves in water to form carbonic acid which is, however. unstable. CO₂ + H₂O H₂CO

Official Tests for Identity

1. Carbon dioxide extinguishes a burning splinter.
2. When the gas is passed through a solution of barium hydroxide, a white precipitate (barium carbonate) is produced. It dissolves with effervescence on the addition of dilute acetic acid

Carbon Dioxide

Medicinal and Pharmaceutical Uses

● Carbon dioxide (5%) is used along with oxygen to

stimulate respiration when it is depressed in

poisoning by carbon monoxide and by drugs such as

morphine.

● It is used for manufacturing some chemicals such as

sodium bicarbonate, sodium carbonate etc.,

● Soda water (water containing carbon dioxide under

pressure) acts as a carminative and promotes

absorption in the stomach.

Nitrous oxide

Preparation :

Nitrous oxide is prepared by heating ammonium

nitrate Since ammonium nitrate may explode

when strongly heated, a mixture of sodium

nitrate and ammonium sulphate may be used.

NH4NO3 = N₂01+ 2H₂O

2NaNO3 + (NH4)2SO4 = 2N₂01+ 4H₂O + Na₂SO

The gas is is collected over hot water. It may be

purified by passing The gas through ferrous

sulphate solution (to remove higher oxides of

nitrogen), caustic soda solution (to remove nitric

acid) and concentrated sulphuric acid (to

remove water vapour).

Nitrous oxide

Standard:

Nitrous oxide contains not less than 95

percent v/v of N₂ 0

Assay:

In this assay also a special apparatus is used:

The essence of this assay is that nitrous oxide

is condensed by using liquid nitrogen and the

non-condensible volume of the gas is

measured.

Storage:

Nitrous oxide is stored under compression in

metal cyclinders of the type conforming to

the appropriate safety regulations and at a

temperature not exceeding 37°C.

The cylinder is painted blue and car ries a

label with the name of the gas or N₂O which is

also painted on the shoulder of cylinder.

Nitrous oxide

Medicinal and Pharmaceutical Uses

● General anaesthetic (inhalation) and

analgesic.

● It is a good inhalation anaesthetic

which also acts as a good analgesic.

● It is used to carry out minor operations

such as tooth ctions and removal of

boils and abscesses.

● It is also used for calming excited

mental patients.

● It is used in a concentration of 60-80%

along with oxygen in a concentration

of 20-40%.

● Since it does not combine with

haemoglobin, nitrous oxide is also used

to measure the cerebral and coronary

blood flow.

Nitrogen

Preparation :

Nitrogen may be obtained either by removing the oxygen from the atomspheric air or by decomposing compounds in which it may occur. Oxygen may be removed from the atmospheric air by any one of the following methods:

● Burning phosphorus in air in a closed container.’ ● Passing air over red-hot copper filings. ● Passsing air through a solution of sodium hydrosulphite (Na2S₂04) which will absorb oxygen. ● Shaking an alkaline solution of pyrogallol with air. Alkaline solution of pyrogallol absorbs oxygen.

Nitrogen may also be prepared by fractional distillation of liquid air Chemically nitrogen is also prepared by oxidation of ammonia with red hot copper oxide.

2NH3 + 3CuO = N₂ + 3H₂O + 3Cu

Nitrogen

Physical and Chemical Properties

● Nitrogen is a colourless, odourless and

tasteless gas. It is slightly lighter than air.

● It is only slightly soluble in water. It is not

poisonous but animals die in an atmosphere of

nitrogen for lack of oxygen

● Nitrogen is a very inert gas.

● With oxygen it combines only in the presence of

lightning or when the mixture is passed through

an electric arc

Tests for Identity

1. Nitrogen is colourless, odourless and tasteless.

2. Nitrogen has no action on litmus and lime water.

3. The flame of a burning wood splinter when

introduced into nitrogen is extinguished (put out).

4. Burning magnesium ribbon continues to burn in a

jar of nitrogen.

Helium

● Helium is an inert gas present in the

atmosphere to the extent of 0.000037% w/w.

● It is present in a concentration of 2% in the

natural gas obtained from Canada and U.S.A. It

is also present in ores of some radioactive

elements such as uranium and thorium.

Whatever may be the source, helium is always

present in the free state.

Medicinal and Other Uses

A mixture of helium (79%) and oxygen (21%) is administered in cases of respiratory distress like asthma because helium of fearless resistance than nitrogen. Because of its lightness and non-inflammability, helium is used for inflating tyres of aeroplanes and for filling balloons.

Helium

Properties : Helium is a colorless, odourless and tasteless gas. After hydrogen it is the lightest substance known. It has a solubility of I in 72 in water. It is monatomic and can be liquefied under pressure.It is adsorbed by coconut charcoal at a low temperature. Liquid helium exhibits some unusual properties.

Standard: Helium contains not less than 98% v/v of He.

Assay: Since likely impurities in helium such as nitrogen can be adsorbed by coconut charcoal cooled by liquid oxygen, a sample of the gas is introduced into a glass bulb containing coconut charcoal cooled by liq uid oxygen. The unabsorbed gas (helium) is pumped out and measured.

Storage: Helium is kept at a pressure of 132 atmospheres i.e., at 2000 lbs per sq. inch in a metallic cylinder capable of withstanding pressure in a cool,dry place, The body and valve end of the gas cylinder should be painted brown. Cylinders containing oxygen and helium mixtures should have the body painted black and the valve end painted white and brown..