Pharmaceutical Chemistry 1 Acid, Base, & Buffer

 Pharmaceutical Chemistry 1

Acid, Base, & Buffer Complete notes

ACID

Arrhenius concept-

According to this concept, those substances which produces free hydrogen ion (H+) in an aqueous solution are called acids.

Example-HCl, HNO3, H2SO4, CH3COOH etc.

HCl + H2o → H⁺+ Cl^-

Bronsted-Lowry concept- According to this concept, those substances which have tendency to donate the proton (H+) by any methods in any solvent are called acids.

Lewis concept- According to this concept, those substances which have tendency to gain lone pair or electron pair are called acids.

Example –AlCl3, SF6, SO3 etc.

Characteristic features of Acids—

• Acids are good conductor of electricity it enhances the electricity when dissolved in aqueous solution.

• Generally, acids are corrosive in nature.

• Acids PH always less than 7.Highly acidic PH damaged our skin and cause severe damage on body part.

• Acids are sour in taste.

• When acids are react with blue litmus paper then it turns red in colour.

• Acids reacts with metals and produces hydrogen gases

• If metal are add in acidic solution then it release bubbles in the solution.

Pharmaceutical uses of acids-

Salicyclic acid—(C7H6O3)

• It is a highly effective chemical to prevent microbial growth on outer layer of skin.

• It is also used for removing warts calluses, psoriasis, dandruff, ringworm, acne and  ichthysis.

• It is mainly used in the preparation of Aspirin. Aspirin is an anticoagulant agent.

Benzoic acid—(C7H6O2)

• It is highly effective antimicrobial (like Bacteria, Fungal) preservative in the pharmaceutical manufacturing.

• Benzoic acid is act as lubricant in the preparation of drug.

• It is also used in the treatment of skin irritation caused by insect’s bites, burn etc.

NOTE- Mixing of Benzoic acid and Salicylic acid (6:3) are used in the preparation of whitfield ointment, which are used in athlete foot disease caused by fungal infection.

• Mixture also act as dermatophytic, fungistatic, keratolytic agent. Acetic acid—(CH3COOH)

• Acetic acid consists of antibiotic properties. So it is used to treats infections caused by microorganism.

• Many drugs preparation it is used as a solvent.

• In vinegar it contains 5-20% of acetic acid .So it is used as a food preservative, drug preservative and pickling agents for vegetables.

• Glacial acetic acid is used as a hypotonic urologic irritation for the urinary bladder.

Nitric acid—(HNO3)

• Nitric acid is used for reducing tooth sensitivity. So it is used in tooth paste preparation.

• It is used as cleaning agent .Nitric acid is treated with hard water and convert into soft water by precipitating the calcium and magnesium impurity.

• It is used in medication to treat cauterize small wounds, warts, verrucae and removing the infected upper tissue of the body part.

Citric acid- (C6H8O7)

• It is widely used in manufacturing of electrolytic solution in the manufacturing unit.So it is also called Mineral acid.

• It also used as cosmetic PH regulator in the formulation.

• In pharmaceutical it is used as taste/flavouring excepient to improve the taste of syrups, elixirs, solution etc.

• It also consists of antimicrobial activity so it is also used in the gargle preparation.

• Natural obtain Citric acid is called  Ascorbic  acid which contain vitamin C.Now days  vitamin C tablet available in market and  use to treating Scurvy disease.

• It is also used as immunity inhancer in Corona pandemic. Note-Citric acid does not contain vitamin C.

Lactic acid- (C3H6O3)

• Lactic acid show antimicrobial activity so it is used as cleaning agent.

• Lactic acid widely used in fermentation and chemical process for growth of microbes in pharmaceutical industry.

• Lactate is the conjugate base of lactic acid and it is used in manufacturing of milk powder.

Sulphuric acid- (H2SO4)

• In pharma it is widely used chemical substance.it is widely used as solvent for synthesis of many active pharmaceutical ingredients.

• It also used to overcome gastric problem like gastric hypoacidity.it is also used as chemotheraputicagent for the treatment of cancer.

• In chemotherapy treatment Sulphuric acid damage the cancer cells DNA and  this process is known as Alkylation  of DNA and  this type of drug known as alkylating antineoplastic agents.

 

Lysergic acid- (C16H16N2O2)

• It is used for preparing LSD (lysergic acid diethylamide).LSD is a hallucinogenic drug that can be derived from the ergot alkaloids.

• It shows psychotropic actions by blocking the serotonin action in brain tissue.

BASE

• Base/Alkali are those substances which provide the hydroxide ions (OH–) in the aqueous solutions.

• It is bitter in taste and slippery/soapy in nature.

Arrhenius concept– According to this concept, those substances which produces free hydroxide ion (OH–) in an aqueous solution are called bases.

Example-NaOH, KOH,Ca(OH)2  etc.

Bronsted-Lowry concept- According to this concept, those substances which have tendency to accept the proton (H+) by any methods in any solvent are called bases.

 Example – SO4^-2, Cl–, O^-2

Lewis concept- According to this concept, those substances which have tendency to donate lone pair or electron pair are called bases.

Characteristic features of base—

• Bases are also a good conductor of electricity it enhances the electricity when dissolved in aqueous solution.

• Bases are soapy/slippery in nature. Bases are react with skin fatty acid layer and provide smooth appearance.

• Bases are bitter in taste. It also consist astringent property so it is also used for blood clot during the injury.

• Bases PH are always more than 7.Its high PH property form the foam with the water so it is used in the manufacturing of soap for removing the dirt from clothes.

• When base are react with red litmus paper then it turns blue in colour.

• Bases does not shows reaction with metal like acid.

• Bases are also acts as electrolyte in aqueous solutions.

Pharmaceutical uses of bases-

Barium hydroxide—[Ba(OH2)]

• Barium hydroxide is a very useful base for manufacturing of gastric related medicine by neutralizing the HCl concentration in G.I.T (gastro intestinal tract)

• Due to its highly basic nature it is used in manufacturing of Enema gel. Enema gel are used as laxative and apply by rectal route.

• Mixture of barium hydroxide used as coating of inner lining of the intestine during the intestinal infection or toxicity.

Potassium hydroxide—(KOH)

• It is used for preparing medicine for treating high blood uric acid.it neutralize the uric acid and form uric acid salt (ppt).

• It is widely used in the wet mount preparation of various clinical sample for microscopic study of Fungi and Fungal elements in skin,hair,nails and even  vaginal secretions.

• It is widely used chemical substances for the preparation of veterinary medicines.

• It is also used for preparing CO2 free environment in the experiment and medicine preparation.

Sodium hydroxide—(NaOH)

• It is a highly  strong base used as preservative.so it help  preventing of mould and  bacterial growth in the  manufacturing unit.It  is also used as cleaner/disinfectant.

• It is also act as solvent in manufacturing of many medicine (like Aspirin).

• It contains anticoagulant properties that can help to prevent the blood clot during the injury.

• It is used as a reagent in the laboratories and used in the preparation of washing soda and soda lime.it is also a co-product of Chlorine.

• It is highly corrosive in nature so it is cause severe burns/allergy on the skin.

• It is widely used in the cholesterol-reducing medications.

Calcium hydroxide—[Ca(OH)2]

• Calcium hydroxide is a strong base which are used as PH adjusters in pharmaceutical industry.

• It is neutralize the acidic PH in stomach so it is used as antacids.

• In the pharm it is used as base, for the preparation of ointments, creams, lotions and suspensions, often as an aqueous solution (lime water).

Calcium hydroxide, Magnesium hydroxide, Aluminum hydroxide—

[Ca(OH)2], [Mg(OH)2], [Al(OH)3].

• It is mainly used as antacids.

• It is used to treat sour stomach, indigestion, upset stomach, heart burn and neutralizes the stomach PH.it also used in the peptic ulcers.

• Those substances also used to reduce phosphate levels in people with certain kidney conditions. it also help to maintaining electrolytic balance.

 

 

 

 

 

BORIC ACID

Formula:  H3BO3

Molar mass: 61.83 g/mol

PH: 5.1

IUPAC ID: Boric acid, Trihydrooxidoboron

Soluble in: Water, Alcohol

Molecular structure:

Synonyms: Boracic acid, Acidim Boricum, Orthoboric acid, Sassolite.

Introduction of Boric Acid:

• The central Boron atom is attached to three hydroxyl groups which are capable to form strong hydrogen bond.

• Boric acid shows antiseptic activity so it is widely used as cleaning/preserving agents at the infected area.

History and Occurrence:

Boric acid was first prepared by Wilhelm Homberg from borax by the action of mineral acids.

• It is the constituents of the many natural occurring minerals like borax, boracite, colemanite etc. Boric acid and its salts found in sea water.

Properties of Boric Acid

Physical properties Of Boric Acid-

• Colour and state — It is colorless transparent or whitish crystalline powder

• Odour and taste — It is odourless with faintly bitter in taste.

• Melting point — 170.9 C.

• Boiling point—300 C.

• Solubility — Its solubility rate is very high in hot water and partially soluble in cold water and freely soluble in glycerine.

• Density — Its density is more than water and nearly equal to -1.435 kg/m3

Chemical properties of Boric acid-

•      When heated to high temperature over 170 C it undergo dehydration to form metaboric acid and pyro boric acid and finally form boron trioxide.

 

Pharmaceutical uses Of Boric Acid

• It shows antiseptic properties so it is widely used as cleaning agent for wound.

• It prevents the eye infections and used in the ophthalmic preparation for providing soothing relief from eye irritation and help to removing pollutants from the eyes such as smog, chlorine, or other chemicals.

• In pharmaceutical it is used to manufacturing of dusting powders and eye lotions.

• It reduces the inflammation of various skin disorders.

Incompatibility and contraindications of Boric Acid-

• Contraindicated in patients with known hypersensitivity to boric acid.

• Boric acid is a weak acid show it is incompatible with base like alkali carbonates and hydroxides.

• It should not take orally or internally and should not apply on broken skin.

• At the high temperature it loses their all properties and dissociate in the boron trioxide.

Storage conditions of Boric Acid

• Boric acid stored in a tightly closed air resistant container at the room temperature and away from the light and moisture.

• It is also keep away from the basic molecule and substance.

BUFFER SOLUTIONS

A solution which resists the change in PH on dilution/addition of small amount of strong acids or bases is called buffer solutions.

• Buffer solution does not change in PH significantly on addition of any acids or bases in small amount.

• A buffer system is composed of weak acids and its salts or weak base and its salts.

• Due to stability of most of weak bases, the system composed of weak bases and its salts is not very useful so weak acids and its salts system are generally used in the processing and manufacturing.

Properties of buffer solutions

• Buffer solutins does not changes PH on dilution of any acids or bases in small amount.

• The buffer PH does not depends on the volume of solution.Hence solution can be diluted without change in PH.

• Buffer solution does not forms complexes with the active ingredients in the pharmaceutical industry.

• The PH of buffer solution remains constant even if it is kept for a long time.

• It does participate in the redox reaction in the manufacturing units.

Classification of Buffer solutions

• On the basis of chemical nature.

1.  Acidic buffer.

2.  Basic buffer.

 

• On the basis of uses.

1.  Analytical use.

2.  Pharmaceutical use.

• Acidic buffer - Acidic buffer is composed of weak acids and its salts.

Example- acetic acid + sodium acetate.

• Basic buffer - Basic buffer are composed of weak base and its salts. Example- mixture of ammonium hydroxide + ammonium chloride. Pharmaceutical uses of buffer solutions

• Buffer solution are widely used as preservatives in the manufacturing of pharmaceutical preparations. It also used as preservatives for foods and fruits.

• In the qualitative analysis of drugs mixture.

• In the quantitative analysis of drugs mixture.

• It is widely used in the biological essay because it is help in the digestion of food by maintaining regular PH in the GIT (gastro intestinal tract).It also participate in metabolism by converting large molecules into smaller.

• In the pharmaceutical industry it is used in manufacturing of medicated shampoos,body lotions,inks dyes,paints drugs,paper,etc

• It is also used in agricultural and dairy products preservatives.

• It also maintain osmotic balance in many experiments.

• Some time it is used as nutritive media for growing microorganisms in pharmaceutical.

Selection of suitable Buffer

• Chemical factor…

• The buffer system should not react with the other chemicals in the preparations and does not affect products stability.

• It is not altered the solubility of chemical compound and does not forms complexes with the active ingredients.

• Pharmacological factors…..

1.  Toxicity of buffers-Buffer solutions are limited use because it provides the nutritive media for growth of microorganisms.so it is eaisly contaminated by the microorganisms and cause toxicity. Example- phosphate buffer.

2.  Effects on the pharmacological action-some time buffer solution are alter the chemical nature of the solution by forming complexes with active ingredients.

 

 

 

 

 

HYDROCHLORIC ACID

Chemical formula— HCl

Molecular mass—36.46g/mol

Molecular structure— H—Cl

Synonyms— Muriatic acid, spirit of salt, chlorohydrin acid.

Introduction of Hydrochloric Acid —

Hydrochloric acid is highly acidic and corrosive in nature. It regulate our gastric PH and helps in the digestion process. Its PH is about 1-3 so its highly acidic nature may cause harmful effect on body parts.

History and preparation—it is one of the mineral acid and used in the both laboratory and industry for a long time.

Glauber prepared this acid in 1648 by heating common salts with concentrated sulphuric acid. Davy in 1810 showed that it is a compound of hydrogen and chlorine.

• In the laboratory it is prepared by (420K) sodium chloride with concentrate sulphuric acid.

NaCl + H2So4 →NaHSo4 + HCl

Physical properties of Hydrochloric Acid —

• Colour and state—it is a colorless gas.

• Odour and taste—it show pungency odour with sour taste.

• Melting and boiling point— M.P- 159K.     B.P- 189K

• Solubility— It is extremely soluble in water and ionised easily.

• Density—1.49 kg/M3

Chemical properties of Hydrochloric Acid —

• HCl reacts with NH3 and gives white fumes of NH4Cl.

NH3 + HCl → NH4Cl

• HCl decompose the salts of weaker acid or carbonates.

Na2Co3 + HCl → 2NaCl + H2O + CO2

• It also reacts with metals and form corresponding chloride.

2Na + HCl → 2NaCl + H2

Pharmaceutical uses Hydrochloric Acid.

• It is widely used as the acidifying agent in the pharma company.

• Dilute HCl is used in the extraction process of alkaloids from crude drugs.

• In G.I.T (gastro intestinal tract) it helps in the digestion process and retard the growth of microorganisms.

• It helps in the manufacturing of many organic and inorganic compounds like (vinyl chloride, ferric acid, aluminum chloralhydrate).

• It is also used in the salts purification.

• Due to its high PH HCl are extremely used as a cleaner.

Chemical incompatibility of HYDROCHLORIC ACID —

• It is incompatible with many substances and highly reactive with strong bases, metals, metal oxides, hydroxides, amines, carbonates etc.

Storage conditions of HYDROCHLORIC ACID —

• It is stored in well closed air resistant containers away from the direct sunlight and moisture at room temperature and keep away from oxidising agent.

SODIUM HYDROXIDE

Chemical formula — NaOH

Molecular mass — 40.01g/mol

Molecular structure — Na—O-H

Synonyms — Caustic soda, Lye, caustic alkali.

Introduction of Sodium Hydroxide —

It is highly versatile substance used in the pharmaceutical industries and other manufacturing processes such as paper, aluminum, soap, cleaners, detergents etc. It is the co-product of chlorine production.

Preparation of Sodium Hydroxide —

(1) By chemical method— Chemically sodium hydroxide are prepared by the reaction of calcium hydroxide and sodium carbonate.

(2) Electrolytic method— Sodium hydroxide is produced using the electrolytic chloro alkali process in which electrolysis of aqueous sodium chloride solution gives chlorine gas and sodium hydroxide.

Physical properties of Sodium Hydroxide —

• Colour and state — It is colorless or white crystalline solid/sticks/pellets.

• Odour and taste — It is odorless with bitter taste.

• Melting and boiling points— M.P—591.55K. B.P—1663.15K

• Solubility— It is highly soluble in polar solvents like water, ethanol, and glycerol and insoluble in ether, acetone and non-polar solvents.

• Density— 2.13g/cm3.

Chemical properties of Sodium Hydroxide —

1) Neutralization reaction.

NaOH + HCl → NaCl + H2O.

2) It reacts with salt of metal. Exp—Ammonium salt

NaOH + NH4Cl → NH4OH + NaCl.

3) Reactions with bicarbonates.

2NaOH + H2CO3 → Na2 CO3 + 2H2O.

Pharmaceutical uses of Sodium Hydroxide-

• It is used as cholesterol lowering agent because it is used in the preparation of cholesterol reducing medications.

• It is used as a anticoagulant agent that can help to prevent the blood clots.

• It is also used in the manufacturing of many pain reliever drug like Aspirin.

• It is highly basic so it is used as industrial solvents and cleaners including flooring stripping products.

• It balances the HCl level in gastric cavity and neutralised the PH.So it is used as the acid reducing substances.

• It is also used in the manufacturing of veterinary products.

• NaOH feels slippery with skin contact due to the process of saponification.

Chemical incompatibility of Sodium Hydroxide-

It is incompatible with the many organic and inorganic acids and most reaction with hylogen.

It also react with metal salt so it is incompatible with salts and alkaloids.

Storage conditions of Sodium Hydroxide-

Due to its highly basic nature it is always reacts with acid so it is stored away from any acid in well closed light resistant containers at room temperature away from light and moisture.

Strong Ammonium hydroxide

Chemical formula—NH4OH or NH3(aq).

Molecular weight—35g/mol or 17g/mol

Molecular structure:

Synonyms—Liquor Ammonia, aqua ammonia, ammonium solution.

Introduction—It is the solution of ammonia in water .when ammonia is dissolved in water, then water molecule donate a proton to the NH3 molecule. This leads to the formation of an ammonium ion.

Preparation and occurrence of Strong Ammonium hydroxide—

Ammonia is made synthetically by the Haber process in which nitrogen are react with hydrogen in the presence of catalyst (molybdenum and iron) maintain at temperature of 500C under 200 atmospheric pressure.

N2 + 3H2 → 2NH3

Ammonia exists in the aqueous solution mainly in the form of NH3 and small quantity reacts with water and forms ammonium hydroxide.

NH3 + H2O →  NH4 OH

Gaseous ammonia was first prepared by joseph Black in 1756 by reacting Ammonium chloride with magnesium oxide.

 

Physical properties of Strong Ammonium hydroxide:

• Colour and state—it is colourless appearance in present in liquid state.

• Odour and taste—It is highly pungent / fishy odour and bitter in taste.

• Boiling and melting point— B.P-310.8K, M.P-215.7 K

• Solubility—it is highly soluble in water

• Density—0.91 g/ cm3

Chemical properties of Strong Ammonium hydroxide—

• Ammonia is a basic solution so it is participate in neutralization reaction by action of acid and forms salts.                 

NH3 +HCl → NH4Cl

• Ammonia can forms ammonium basic salts through a reaction known as ammonolysis.

HgCl2 + NH3 → Hg(NH2)Cl + HCl

• When the ammonia gas is passed over the heated oxides of metals nitrogen gas is release.

3CuO + 2NH3 → 3Ca + 3H2O + N2

Pharmaceutical uses of Strong Ammonium hydroxide:

• Dilute solution of ammonia (10%) is a common reagent and used as base.

• Ammonium salts are used in the preparation of detergents, soap, ink etc.

• It is used as antacid/ counterirritant and stimulant in the respiratory infection/ problem.

• Dilute (1-3%) ammonia is also used as ingredients of numerous cleaniy agents including many windows cleaning formulas.

• It is also used in the production of Organic and inorganic chemicals containing nitrogen and it is the important tool in the manufacturing process of chemical fertilizers.

Chemical incompatibility of Strong Ammonium hydroxide

• An ammonia is a base so it is incompatible with. Acid.it is also incompatible with salts of metal such as iron, zinc, and copper etc.

• It is also incompatible with alkaloids like Quinine and tannins.

Storage conditions of Strong Ammonium hydroxide —

Ammonia are very volatile at room temperature so it is store in the well closed container away from the light, and temperature not exceeding more than room temperature.

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