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PHARMACEUTICAL CHEMISTRY
Gastrointestinal Agents
Dr. Mymoona Akhter Lecturer Dept. of Pharmaceutical Chemistry Jamia Hamdard Hamdard Nagar New Delhi-
CONTENTS
Acidifying Agents Dilute Hydrochloric Acid Antacids Sodium Bicarbonate Aluminium Hydroxide Aluminium Phosphate Dihydroxy Aluminium Ammonium Acetate Dihydroxy Aluminium Sodium Carbonate Calcium Carbonate Tribasic Calcium Phosphate Magnesium Carbonate Magnesium Oxide Magnesium Phosphate Magnesium Trisilicate Protectives and Adsorbents Bismuth Subcarbonate Bismuth Subgallate Kaolin Activated Charcoal Saline Cathartics Sodium Acid Phosphate Disodium Hydrogen Phosphate Sodium Potassium Tartarate Magnesium Sulphate Calomel Sulphur Precipitated Sulphur
Keywords Acidifying agents, antacids, saline cathartics
Agents used to treat gastrointestinal disturbance are known as gastrointestinal agents. Various inorganic agents used to treat GIT disorders include:
- Products for altering gastric pH i.e. acidifying agents and antacids
- Protectives and adsorbents
- Saline cathartics or laxatives
Acidifying Agents The pH of stomach is 1.5 -2 when empty and rises to pH 5-6 when food is ingested. The pH of stomach is so low because of the secretion of HCl. Gastric HCl act by destroying the bacteria in the ingested food and drinks. It softens the fibrous food and promotes the formation of the proteolytic enzyme pepsin. This enzyme is formed from pepsinogen at acidic pH (>6). Pepsin helps in the metabolism of proteins in the ingested food. Therefore lack of HCl in the stomach can cause Achlorhydria. Two types of achlorhydria are known:
where the gastric secretion is devoid of HCl, even after stimulation with histamine phosphate
where gastric secretion is devoid of HCl, but secreted upon stimulation with histamine phosphate.
The cause of achlorhydria in first case may be subtotal gastrectomy, atrophic gastritis, carcinoma, gastric polyp etc while in later case it may be chronic nephritis, tuberculosis, hyperthyroidism, chronic alcoholism, sprue, pellagra etc. The symptoms vary with associated disease but they generally include mild diarrhoea or frequent bowl movement, epigastric pain and sensitivity to spicy food.
Achlorhydria can be treated by various acidifying agents like ammonium chloride, dilute HCl, Calcium chloride etc.
Dilute Hydrochloric Acid HCl M.W 36.
I.P. Limit: It contains not less than 9.5% and not more than 10.5% w/w of HCl.
The acid should be diluted with 25-50 volumes with water or juice and sipped through a glass tube to prevent reaction upon dental enamel. It is taken during or after meals given in conjunction with iron therapy in hyper chromic anemia.
Preparation: It is prepared by mixing 274gm of HCl and 726 gm of purified water.
Test for Identification:
- When added to KMnO 4 with dilute nitric acid, chlorine is evolved.
- To acidified solution add silver nitrate solution, shake and allow to stand, curdy white precipitate is formed, which is insoluble in HNO 3 but soluble after being washed with water in ammonium hydroxide from which it is reprecipitated by the addition of HNO 3.
Assay: Weigh accurately 6gm, add 30 ml of distilled water mix and titrate with 1N NaOH using methyl red as indicator. Each ml of 1N NaOH is equivalent to 0.03646gm of HCl.
Systemic absorption leads to alkalosis, may worsen edema and congestive heart failure because of sodium ion load.
Non Systemic antacids They are insoluble and poorly absorbed systemically. In Magnesium salt, Magnesium carbonate is most water soluble and reacts with HCl at a slow rate, while Magnesium hydroxide has low solubility and has the power to absorb and inactivate pepsin and to protect the ulcer base. Aluminium hydroxide is a weak and slow reacting antacid. The aluminium ions relax smooth muscles and cause constipation. It absorbs pepsin at pH>3 and releases it at lower pH. It also prevents phosphate absorption. Calcium carbonate is a potent antacid with rapid acid neutralizing capacity, but on long term use, it can cause hypercalcemia, hypercalciuria and formation of calcium stone in kidney.
Every single compound among antacid have some side effect especially when used for longer period or used in elderly patients. To avoid certain side effects associated with antacids, combinations of antacids are used such as :
(i) Magnesium and aluminium containing preparation e.g. magnesium hydroxide a fast acting antacid with aluminium hydroxide which is a slow acting antacid. (ii) Magnesium and calcium containing preparation where one is laxative and the later one is constipative in nature.
Compounds used as Antacids
(i)Sodium Bicarbonate (Baking soda) NaHCO 3 M.W. 84.
I.P. limit: It contains not less than 99% and not more than 101% of NaHCO 3
Properties: White crystalline powder, odorless, with saline and slight alkaline taste, Stable in dry air, sparingly soluble in water, insoluble in alcohol.
Preparation:
- By passing strong brine containing high concentrations of ammonia through a carbonating tower where it is saturated with carbon dioxide under pressure. The ammonia and carbon dioxide reacts to form ammonia bicarbonate which is allowed to react with NaCl to precipitate NaHCO 3 which is separated by filtration. NH3 + H 2 O + CO 2 NH 4 HCO 3 NH 4 HCO 3 + NaCl NaHCO 3
- It can also be prepared by covering sodium carbonate crystals with water and passing carbon dioxide to saturation. Na 2 CO 3 + H 2 O + CO 2 NaHCO 3
Test for identification: To 5ml of 5%w/v solution in carbon dioxide free water add 0.1ml phenolphthalein solution a pale pink color is obtained. On heating a gas is evolved and the solution turns red.
For Sodium: 1.To sample solution add 15% w/v potassium carbonate, heat, no precipitate is obtained add potassium antimonite solution heat to boiling, cool and if necessary scratch the inside of test tube with a glass rod, a dense white precipitate is produced.
- Acidified the sample solution with 1M acetic acid and add excess of magnesium uranyl acetate solution yellow crystalline precipitate is obtained.
For bicarbonate: to sample add magnesium sulphate no precipitate is produced. On boiling a white colored precipitate is formed.
Assay: Weigh accurately 1gm and dissolve in 20ml of water, titrate the solution with 0.5N sulphuric acid using methyl orange as indicator. Each ml of 0.5N sulphuric acid ≡0.0425gm of NaHCO 3
Use: It is used as antacid, and in electrolyte replacement.
(ii) Aluminium Hydroxide Al(OH) 3 M. W. = 78.
Aluminium hydroxide gel is an aqueous suspension of hydrated aluminium oxide with different amounts of basic aluminium carbonate and bicarbonate.
I.P. limit: It contains not less than 3.5% and not more than 4.4% of Al 2 O 3
Properties: Aluminium hydroxide is a white, light odorless, tasteless amorphous powder. It is soluble in dilute mineral acids and in solution of alkali hydroxides but practically insoluble in water. It forms gel on prolonged contact with water at pH 5.5-8.0. It absorbs acids and carbon dioxide. The aluminium hydroxide gels are ideal buffers in the pH 3-5 range due to its amphoteric nature.
Preparation: It is prepared by dissolving sodium carbonate in hot water and the solution is filtered. To the filtrate add clear solution of alum (aluminium salt, chloride or sulphate) in water with constant stirring. Add more of water and remove all gas. The Aluminium Hydroxide precipitate out, collect the precipitate, wash and suspend in sufficient purified water flavoured with 0.01% peppermint oil and preserve with 0.1% sodium benzoate. Al 2 (SO 4 ) 3 + 3Na 2 CO 3 + 3H 2 O 2Na 2 SO 4 + Al(OH) 3 + 3CO 2
Test for identification: A solution in 2N HCl gives the characteristic reactions of aluminium salts. To sample add 5drops of freshly prepared 0.05%w/v solution of quinalizarin in 1% w/v solution of NaOH heated to boiling, cool, acidify with excess of acetic acid a reddish violet color is produced.
Assay: Accurately weigh 5gm and dissolve in 3ml HCl by warming on water bath, cool to below 20 °C and dilute to 100ml with water. To 20ml of this solution add 40ml of 0.05M disodium EDTA, 80ml water, 0.15ml methyl orange/red and neutralize by the dropwise addition of 1M sodium hydroxide. Again warm on water bath for 30 min, add 3gm hexamine and titrate with 0.05M lead nitrate using 0.5ml xylenol orange as indicator. Each ml of 0.05M disodium EDTA ≡0.002549 gm of Al2 O
Uses: Aluminium hydroxide is used as antacid in the management of peptic ulcer, gastritis, gastric hyperacidity. It is also used as skin protectant and mild astringent.
(iii) Aluminium Phosphate AlPO 4 M.W. =122.
Aluminium phosphate consists of hydrated aluminium orthophosphate.
Assay: Transfer about 2.5gm of accurately weighed dihydroxy aluminium ammonium acetate and add 15ml of HCl and warm if necessary, to dissolve the sample completely. Transfer the solution with the aid of water to 500ml volumetric flask and dilute with water to volume and mix. Transfer 20ml and add 25ml 0.05M disodium EDTA and 20ml of acetic acid ammonium acetate buffer. Heat near boiling for 5min, cool and add 50ml of alcohol and 2ml of dithizone. Titrate with 0.05M zinc sulphate until green violet color turns rose pink. Perform blank and calculate the volume consumed by sample. Each ml of 0.05M disodium EDTA≡ 2.549 mg of Al 2 O 3
Use: It is used as antacid.
(v) Dihydroxy Aluminium Sodium Carbonate CH 2 Al Na O 5 M.W.=143.
I.P limit: It contains not less than 90% and not more than 110.0% of Al 2 O 3
Preparation: It is prepared by reaction between an alkoxide and sodium bicarbonate in water.
Test for Identification:
For aluminum: A solution in 2N HCl gives the reactions characteristic of aluminium salts. To sample add 5drops of freshly prepared 0.05%w/v solution of quinalizarin in 1% w/v solution of NaOH heated to boiling, cool, acidify with excess of acetic acid, a reddish violet color is produced.
For Carbonate: Suspend sample in 2ml of water in a test tube, add 2M acetic acid close the tube immediately with a stopper fitted with a glass tube bent at two right angles, heat gently and collect the gas in 5ml of 0.1M barium hydroxide a white precipitate is formed which is dissolves on addition of excess of dilute HCl.
For Sodium: To sample solution add 15% w/v potassium carbonate, heat, no precipitate is formed add potassium antimonite solution heat to boiling, cool and if necessary scratch the inside of test tube with a glass rod, a dense white precipitate is produced.
Assay: Weigh accurately powder not less than 200mg add 10ml of 2N HNO 3 cover and boil for 1 min, add 25ml of 0.1M disodium EDTA again boil for 1min cool, then add 10ml acetic acid ammonium acetate buffer and 50ml of acetone and 2ml of dithizone, adjust pH to 4.5 by the addition of ammonium hydroxide and titrate with 0.05M zinc sulphate maintaining pH at 4.5. Perform blank and calculate the volume consumed by sample. Each ml of 0.05M disodium EDTA≡ 5.098 mg of Al 2 O 3
Use: It is used as antacid.
(vi)Calcium Carbonate (precipitated chalk) Ca CO 3 M.W. = 100
Calcium carbonate is found in nature as limestone, marble, calcite, vaterite, aragonite and shell of sea animals.
I.P. limit: It contains not less than 98% and not more than 100.5% with reference to dried substance.
Properties: It occurs as a white, odorless tasteless microcrystalline powder which is stable in air. It exists in two crystal form and both are of commercial importance, one Aragonite and other is Calcite.
Precipitated chalk is prepared as a fine precipitate by adding a solution of ammonium carbonate and ammonia or sodium carbonate to a solution of calcium nitrate.
Preparation:
- It can be prepared by mixing and boiling calcium and sodium carbonate solution and allowing the resulting precipitate to settle. The precipitate is collected, washed with boiling water until free from chloride and dried. CaCl 2 + Na 2 CO 3 CaCO 3 + 2Na Cl
- By passing carbon dioxide through lime water CaO + CO 2 + H 2 O CaCO 3
Test for Identification: For Calcium: Dissolve substance in 5M acetic acid and add 0.5ml of potassium ferrocyanide solution. The solution remains clear. Add ammonium chloride white crystalline precipitate is formed.
For Carbonate: Suspend sample in 2ml water in a test tube, add 2M acetic acid close the tube immediately with a stopper fitted with a glass tube bent at two right angles, heat gently and collect the gas in 5ml of 0.1M barium hydroxide a white precipitate is formed which is dissolves on addition of excess of dilute HCl.
Assay: Accurately weigh 0.1gm, dissolve in 3ml of dilute HCl, add 10ml of water. Boil the solution for 10min, cool, dilute with 50 ml with water. Titrate the solution with 0.05M disodium EDTA to with a few ml of the expected end point and add 8ml of NaOH solution and 0.1g of calcon mixture. Continue the titration until the color changes from pink to blue. Each ml of 0.05M disodium EDTA≡ 0.005004g of CaCO 3
Uses: It is used as fast acting antacid, in calcium deficiency, dentrifries and in combination with magnesium containing antacids due to its constipative properties.
(vii)Tribasic Calcium Phosphate CaO 3 P 2 O 5 H 2 O M.W.=328.
I.P limit: Tribasic calcium phosphate consist of variable mixture of calcium phosphate having approximate composition of 10CaO 3P 2 O 5 H 2 O not less than 34% and not more than 40% of calcium and an amount of phosphate equivalent to not less than calcium phosphate calculated with reference to ignited substance.
Properties: It is a white odourless, tasteless, amorphous powder practically insoluble in water, alcohol or acetic acid but readily soluble in dilute HCl and HNO 3
Preparation:
- It is manufactured from bones which are calcined until white, powdered and digested with sulphuric acid. The insoluble tribasic calcium phosphate is converted to soluble phosphoric acid and insoluble calcium sulphate. The solution is filtered and the filtrate treated with calcium hydroxide to precipitate calcium phosphate.
- Decomposition of calcium chloride and sodium phosphate in presence of aqueous ammonia at high temperature yield calcium phosphate. The white precipitate is filtered washed and freed from chloride and dried.
Assay: Accurately weigh 15g of magnesium carbonate and dissolve in a mixture of 20ml of water and 2ml 2M HCl. To this solution add 50ml of water and 10ml strong ammonia ammonium chloride solution titrate this with 0.05M disodium EDTA using mordant black II mixture as indicator until blue color is obtained. Each ml of 0.05M disodium EDTA≡ 0.002015g MgO
Uses: It is used as antacid and mild laxative. It is used as pharmaceutical aid (dispensing volatile oil for use in inhalants).
(ix) Magnesim Oxide (Magnesia) MgO M.W. = 40.
I.P. limit: It contains not more than 98% of magnesium oxide
It occurs in nature as mineral periclase. It occurs in two varieties heavy magnesium oxide which is relatively dense white powder with 15 g occupying volume of about 30ml while light magnesium oxide is very bulky with 15 g occupying volume of about 150ml.
Properties: Both heavy and light magnesium oxide are odorless taste slightly alkaline, practically insoluble in water yield a solution which is alkaline. It readily dissolves in dilute acids with slight effervescence. In presence of acid, the oxide forms the magnesium hydroxide, therefore the chemistry and pharmacology are same as those of magnesium hydroxide.
Preparation:
- It can be prepared by heating gently magnesium carbonate to redness. (MgCO 3 ) 4 Mg(OH) 2 5H 2 O MgO + CO 2 + H 2 O
- It is also prepared by heating light magnesium carbonate to redness. (MgCO 3 ) 4 Mg(OH) 2 3H 2 O 4MgO + 3CO 2 + 3H 2 O
Test for identification: For Magnesium: to solution of sample add dilute nitric acid solution a white precipitate is produced that is redissolved by adding 1ml of 2M ammonium chloride, add 0.25M disodium hydrogen phosphate a white crystalline precipitate is produced.
Assay: The assay of magnesium oxide is performed by complexometry. Accurately weigh 15g of magnesium oxide and dissolve in a mixture of 20ml of water and 2ml 2M HCl. To this solution add 50ml of water and 10ml strong ammonia ammonium chloride solution titrate this with 0.05M disodium EDTA using mordant black II mixture as indicator until blue color is obtained. Each ml of 0.05M disodium EDTA≡ 0.002015g MgO
Uses: It is used as antacid and laxative. It is ingredient of universal antidote along with tannic acid and charcoal. It is used for compounding and preserving fluid extract because of its absorptive power.
(x)Magnesium Phosphate Mg 3 (PO 4 ) 2 5H 2 O M.W. = 352.
I.P. limit: It contains not less than 98% and not more than 101.5% substance ignited at 425°C to constant weight.
Properties: It is white, odourless, tasteless powder readily soluble in dilute mineral acids but practically insoluble in water. The chemistry is same as tribasic calcium phosphate.
Test for Identification: For Magnesium: to solution of sample add dilute nitric acid solution a white precipitate is produced that is redissolved by adding 1ml of 2M ammonium chloride, add 0.25M disodium hydrogen phosphate a white crystalline precipitate is produced.
For phosphate: To neutral sample solution add silver nitrate solution, a light yellow precipitate forms, the color of which is not changed by boiling and is readily soluble in 10M ammonia and dilute HNO 3.
Assay: Weigh accurately 200mg previously ignited to 425°C to constant weight and dissolve in mixture of 25ml of water and 10ml of 2N HNO 3. Filter if necessary, wash any precipitate add sufficient 6Nammonium hydroxide to the filtrate to produce a slight precipitate and then add 1ml of 2N HNO 3. Adjust temperature to 50° add 7ml ammonium molybdate and maintain temperature for 30min with occasional stirring. Wash the precipitate once or twice with water by decantation. Transfer precipitate to the filtrate, wash with KNO 2 solution until the last washing is not acid to litmus. Transfer precipitate and filter to precipitate vessel add 50ml of water and 40ml of 1N NaOH, agitate until the precipitate is dissolved, add phenolphthalein and titrate excess of alkali with 1N H 2 SO 4. Each ml of 1N NaOH ≡ 5.716mg of magnesium phosphate.
Uses: It is used as antacid and laxative.
(xi)Magnesium Trisilicate 2MgO 3SiO, xH 2 O M.W. (anhydrous) =260.
I.P. limit: It contains not more than 29% of magnesium oxide and not more than 65% of silicon dioxide both calculated with reference to the ignited substance.
Properties: Fine, white, odorless, tasteless powder, free from grittiness. Magnesium silicate hydrate is a compound of magnesium oxide and silicon dioxide with varying amount of water.
Preparation: It is prepared by precipitation from solution of magnesium sulphate and sodium silicate. 2MgSO 4 + 2Na 2 O 3SiO 2 + X H 2 O 2MgO 3SiO 2 XH 2 O + Na 2 SO 4 + H 2 O
Test for identification: For Magnesium: to solution of sample add dilute nitric acid solution a white precipitate is produced that is redissolved by adding 1ml of 2M ammonium chloride, add 0.25M disodium hydrogen phosphate a white crystalline precipitate is produced. For silicate: in a lead or platinum crucible mix by means of a copper wire to obtain a thin slurry the prescribed amount (0.25gm) of substance with 10mg of sodium fluoride and a few drops of sulphuric acid cover the crucible with thin transparent plate of plastic under which a drop of water is suspended and warm gently within a short time a white ring is formed around the drop of water
Assay: For Magnesium Oxide: Weigh accurately 1gm substance and dissolve in 35ml of water allow to stand for 15min on water bath. Cool the contents to room temperature filter and wash the residue with water and dilute the combined filtrate and washing to 250ml with water. Neutralize 50ml of this solution with about 8ml of 10M NaOH and then add 10ml ammonia buffer pH 10, 50mg mordant black II mixture. Heat the contents to 40 °C and titrate with
(ii) Bismuth Subgallate I.P limit: It contains not less than 52% and not more than 57% of bismuth trioxide calculated with reference to the substance dried to constant weight at 105°C.
Bismuth subgallate is a basic salt of bismuth. It is amorphous, bright yellow powder, odorless, tasteless. Practically insoluble in water, ether, ethanol but readily dissolves in hot mineral acids with dcomposition and in solution of alkali hydroxides.
Test for Identification: To 0.5gm sample add 10ml 2N HCl and heat to boiling for 1min, cool and filter, if necessary. To 1ml add 20ml of water a white or slightly yellow precipitate is formed which on addition of 0.05-0.1ml of sodium sulphate solution turns brown
Preparation: It is prepared from bismuth nitrate and gallic acid in acetic acid medium. The acetic acid can be replaced by mannitol or glycol.
Assay: Dry about 1gm at 105°C to constant weight, add nitric acid dropwise with stirring and warm until solution is complete. Evaporate the solution to dryness and carefully ignite the residue to constant weight. The residue represents the quantity if Bi 2 O 3 in the weight of substance taken.
Use: It is used as astringent, antacid and protective.
(iii) Kaolin Al 2 O 3 2SiO 2 2H 2 O
Heavy kaolin is purified natural hydrated aluminium silicate of variable composition. Light kaolin is native hydrated aluminum silicate freed from most of its impurities by elutriation and dried. It may contain a suitable dispersing agent.
Preparation: Kaolin is widely distributed in nature contaminated with ferric oxides. It is prepared when the rock is mined, evacuated and the impurities are washed with water and then powdered. The rock is elutriated with water and large sized particles are separated. The turbid liquid is allowed to settle; heavy kaolin containing large particles and colloidal kaolin containing particles of small size are separated and dried. For pharmaceutical use it is purified by treatment with HCl and H 2 SO 4 or both and then washed with water.
Test for Identification: Fuse 2gm of substance with 4gm anhydrous sodium carbonate. Warm residue with water and filter, acidify the filtrate with HCl evaporate to dryness and warm the residue with dilute HCl, residue of silica is obtained and the acid solution after neutralization gives reaction for aluminum.
For aluminium: To 0.5 gm in a metal cucible add 1gm HNO 3 and 3gm anhydrous sodium carbonate, heat to melt and allow cool, adding 20ml of boiling water to this residue and filtering. To filtrate add 1ml of 10M NaOH and filter. To filtrate add 3ml of ammonium chloride solution a gelatinous white precipitate is obtained. For silicate: Fuse 1gm of substance with 2g anhydrous sodium carbonate and warm the residue with 10ml of water, filter, wash with water and reserve the residue. To combined filtrate and washings add 3ml of HCl a gelatinous precipitate is obtained.
Use: It is used as adsorbent in diarrhoea caused by agents capable of being absorbed e.g due to food poisoning. Also used in chronic ulcerative colitis. As poultice, dusting powder, clarifying and decolorizing medium, as filtering medium, as tablet diluent.
(iv) Activated Charcoal Absorbing power should not be less than 40% of weight of phenazone calculated with reference to the dried substance.
Preparation: Decolorizing charcoal is obtained from magnesium matter by suitable carbonization process intended to confer a high absorbing power.
Test for identification: When heated to redness burns slowly without flame.
Assay: To 0.3gm of substance add 25ml of freshly prepared 1% w/v solution of phenazone, shake thoroughly for 15min. filter the solution and discard the first 5ml of the filtrate. To 10ml of the filtrate add 1gm potassium bromide, 20ml of 2M HCl and titrate with 0.0167M potassium borate using 0.1ml of ethoxydrysoidine HCl solution as indicator. The endpoint is change of color from reddish pink to yellow pink. Repeat the titration with phenazone only using 10ml of phenazone. Calculate the % of phenazone absorbed using expression
2.353 (a-b) /w
where w is weight in gms of sample, a is volume consumed during first titration, b is volume consumed by phenazone only.
Saline Cathartics Saline cathartics or purgatives are agents that quicken and increase evacuation from the bowl. Laxatives are mild cathartics. Cathartics are used: ¾ to ease defecation in patients with painful hemorrhoids or other rectal disorders and to avoid excessive straining and concurrent increase in abdominal pressure in patients with hernias Or ¾ to avoid potentially hazardous rise in B.P. during defecation in patients with hypertension, cerebral coronary or other arterial disease Or ¾ to relieve acute constipation Or ¾ to remove solid material from intestinal tract prior to certain roentgenographic studies.
Laxative should only be used for short term therapy as prolonged use may lead to loss of spontaneous bowl rhythm upon which normal evacuation depends, causing patient to become dependent on laxatives, the so called laxative effect.
Constipation is the infrequent or difficult evacuation of the feces. It may be due to a person resisting the natural urge to defecate, causing the fecal material which remains in the colon to lose fluid and to become relatively dry and hard. Constipation can also be due to intestinal atony, intestinal spasm, emotions, drugs and diet. Many a time constipation can be helped by eating food such as natural laxatives or food with large roughages. Four types of laxatives are known:
- Stimulants 2. Bulk forming
- Emollient 4. Saline cathartics
Stimulants act by local irritation on the intestinal tract which increase peristaltic activity. They include phenolphthalein, aloin, cascara extract, rhubarb extract, senna extract, podophyllin, castor oil, bisacodyl, calomel etc.
Assay: Weigh accurately 2.5 gms dissolve in 40ml water and titrate with carbonate free 1M NaOH. Determine end point potentiometrically. Each ml of 0.5M sodium hydroxide ≡ 0.0780g of NaH 2 PO 4 2H 2 O
Use: It is used as saline cathartic and as buffer in pharmaceutical preparations. As urinary acidifier, source of phosphorous.
(ii)Disodium Hydrogen Phosphate (phosphor soda) Na 2 HPO 4 12H 2 O M.W. = 358.
I.P limit: It contains not less than 98.0% and not more than 101% of NaH 2 PO 4 calculated with reference to the dried substance.
Properties: Colorless, odorless, crystalline powder. Soluble in water and practically in soluble in alcohol. Very efflorescent.
Preparation:
- It is prepared by reaction of orthophosphoric acid calculated quantity of sodium hydroxide. 2NaOH + H 3 PO 4 Na 2 HPO 4 + 2H 2 O
- From bone ashes or mineral phosphorite, which is treated with sulphuric acid
Assay: Weigh accurately 4gm of substance and dissolve in 25ml of water add 25ml 1N HCl and titrate potentiometrically with 1M NaOH to first inflection point of the pH curve (n1) continue titration until second inlfection of curve is reached. The total volume of NaOH required is n2 ml. calculate percent content from the expression 1420(25-n1)/w (100-d) d is percentage of water content.
Use: Widely used as saline cathartic. Orally as antihypercalcemic It is a pharmaceutical aid used as buffering agent.
(iii) Sodium Potassium Tartarate COONa CH(OH), CH (OH) COOK 4H 2 O M.W. = 282.
I.P limit: It contains not less than 99.0% and not more than 102% of C 4 H 4 KNa calculated on the anhydrous basis.
Preparation : It is prepared by boiling a solution of sodium carbonate and potassium bitartarate for sometime and allowing the reaction mixture to stand at 60°C. The solution is filtered, concentrated and crystallized.
COOK
COOK
HO
HO
(^2) + Na 2 CO 3
COONa
COOK
HO
HO
(^2) + CO 2 + H 2 O
Test for Identification: For potassium : To 1ml of solution add 1ml dilute acetic acid and 1ml of 10% w/v sodium cobalt nitrite a yellow color produced.
For sodium: To 2ml of solution of 2ml of 15% w/v of K 2 CO 3 heat to boil, no precipitate is produced. Add 3ml of potassium antimonite solution and heat to boil. Allow to cool in ice and if necessary scratch the inside of the test tube with glass rod white precipitate is produced.
For tartarate: 1) Warm the substance with sulphuric acid charring occurs and carbon monoxide which burns with blue flame is evolved.
- To 5ml of sample solution add 1% w/v solution of ferrous solution and 0.05ml of hydrogen peroxide (10 vols) a transient yellow color is produced. After color disappears add 2M NaOH intense blue color is produced.
Assay: Weigh accurately 2g and heat until carbonized, cool and boil the residue with 50ml of water and 0.5N sulphuric acid (50ml). It is filtered washed with water and the filtrate and washing are titrated with 0.5N NaOH using methyl orange as indicator. Each ml of 0.5M sodium hydroxide ≡ 0.07056g
Uses: It is used as laxative, food additive, as stabilizer in cheese and meet products.
(iv) Magnesium Sulphate MgSO 4 7H 2 O M.W. = 246.
I.P. limit: It contains not less than 99.0% and not more than 100.5% of magnesium sulphate calculated with reference to dried substance.
Properties: It forms colorless prismatic crystals. It dissolves in water, is practically insoluble in alcohol. It has cooling saline bitter taste.
Preparation:
- It can be prepared by neutralizing hot dilute sulphuric acid with magnesium or its oxides or carbonate. The solution is filtered; the filtrate is concentrated and recrystallized. Mg CO 3 + H 2 SO (^4) MgSO 4 + H 2 O + CO 2
Mg O + H 2 SO (^4) MgSO 4 + H 2 O
- On commercial scale it is manufactured by reacting sulphuric with dolomite. Magnesium sulphate so formed is dissolved in the solution and the sparingly soluble calcium sulphate is deposited. The liquid is filtered the filtrate is concentrated and crystallized. Mg CO 3 Ca CO 3 + 2H 2 SO 4 MgSO 4 +CaSO 4 + 2 H 2 O + 2CO (^2) Dolomite Test for Identification: For magnesium : To solution of sample add dilute nitric acid solution a white precipitate is produced that is redissolved by adding 1ml of 2M ammonium chloride, add 0.25M disodium hydrogen phosphate a white crystalline precipitate is produced.
For sulphate : To 5ml of sample solution add 1ml of dilute HCl and 1ml barium chloride solution white precipitate. Add 1ml of iodine solution to the suspension, the suspension remains yellow (distinction from sulphites and dithionites) but decolorizes on adding stannous chloride (distinction from iodates).
Assay: Weigh accurately about 6.3gm of sample dissolve in 50ml of water, add 10ml of strong ammonia ammonium chloride solution and titrate with 0.05M disodium EDTA using 0.1gm of moderate black II mixture as indicator until blue color is obtained. Each ml of 0.05M disodium EDTA≡ 0.00602 gm of MgSO 4
Uses: It is used as osmotic laxative, in treatment of electrolyte deficiency, in wet dressing in boils, in treatment of cholecystitis, sea sickness, hypertension etc.
A yellow amorphous solid which is nearly insoluble in any solvent. It is usually very fine divided and difficult to filter. It may form a colloidal solution in water, known as milk of sulphur.
(vii)Precipitated sulphur (milk of sulphur) Sulphur reacts with boiling solution of metal hydroxide to fom mixture of metal sulphides and thiosulphate. 3Ca(OH) 2 + 12S 2CaS 5 + CaS 2 O 3 + 3H 2 O
Sulphur can be precipitated by the addition of HCl 2CaS 5 + CaS 2 O 3 + 6HCl 3CaCl 2 + S + 3H 2 O
It is very fine, pale yellow amorphous or microcrystalline powder, without odor or taste. It is soluble in carbon disulphide, insoluble in water and alcohol.
Uses: 1%, 5%, 10% and 20% precipitated sulphur ointments are used as mild irritant and antimicrobic agent in the treatment of skin diseases, e.g as fungicide, paraceticide, keratolytic etc.
Suggested Readings:
- J Bassett, R C Denney, G H Jeffery, J Menndham, Vogel’s Textbook of Quantitative Inorganic Analysis, The ELBS and Longman, London
- J.C. Block et al, Inorganic Medicinal and Pharmaceutical Chemistry, Lee Febiger, Philadelphia PA
- A H Backett and JB Stenlake, Practical Pharmaceutical Chemistry, Vol I and II, The Athlone Press of the University of London
- Parmacopoeia of India, Govt of India, Ministry of Health, Delhi
