Organic pharmaceutical chemistry third stage EXP.1 Assay of Sodium Benzoate Sodium benzoate has the chemical formula C7H5O2 Na with Mwt. 144.1, it is the sodium salt of benzoic acid and exists in this form when dissolved in water. It can be produced by the neutralization of benzoic acid with sodium hydroxide. Sodium benzoate can also be prepared by adding benzoic acid to a hot concentrated solution of sodium bicarbonate until effervescence ceases. The solution is then evaporated, cooled and allowed to crystallize or evaporate to dryness, and then granulated. C6H5COOH + NaOH C6H5COOH + NaHCO3 C6H5COONa + H2O C6H5COONa + H2CO3 Physical properties 123456- It is a white crystalline powder. Density(1.44). Boiling point not applicable. Melting point >300℃. Odorless compound that has a sweet. Soluble in water (1gm/ 2mL water). Organic pharmaceutical chemistry third stage Chemical properties 1- In combination with ascorbic acid (vitamin C) sodium benzoate and potassium benzoate form benzene, most beverages that contained both ascorbic acid and benzoate had benzene levels that were below those considered dangerous for consumption by the World Health Organization (5 ppb), Heat and light can increase the rate at which benzene is formed. 2- Sodium benzoate is heated with soda-lime and when it gets decarboxylated (removal of carbon dioxide) benzene is obtained. 3- Sodium benzoate reacts with hydrochloric acid to produce benzoic acid. C6H5COONa + HCl NaCl + C6H5COOH Pharmaceutical applications 1- Sodium benzoate has antibacterial and antifungal properties and 2- 345- uses as preservative in pharmaceutical formulation including oral preparation in concentrations up to 0.5 %. It is also a common ingredient of cough preparations. Sodium benzoate is used as a treatment for urea cycle disorders due to its ability to bind amino acids. This is leads to excretion of these amino acids and a decrease in ammonia levels. Sodium benzoate may be uses on therapy of schizophrenia. Total Positive and Negative Syndrome Scale scores dropped by 21%. Sodium benzoate is use in cosmetic products like mouthwash, toothpaste, deodorant, lotion, and shampoo. Notes Sodium benzoate is an antimicrobial active against most yeast and bacterial strains. It works by dissociating in the system and producing benzoic acid. Benzoic acid is highly toxic to microbes; however, it is less effective against molds. Overall, it is more effective as the pH of a system is reduced with the optimal functional range between pH 2.5-4.0. The antimicrobial effect is also enhanced by the presence of sodium chloride. Organic pharmaceutical chemistry third stage Chemical principle: Sodium benzoate is a salt derive from a weak acid and a strong base, so its aqueous solution is alkaline. Therefore, sodium benzoate is assay by using a standard N/2 HCl solution in acid base titration. Procedure: 1- Fill the burette with N/2 HCl . 2- Put 10 ml of an unknown sample of sodium benzoate solution in a clean conical flask. 3- Add 25 ml of DW and 15 ml of ether. 4- Add 6 drops of bromophenol blue. 5- Start titration by adding HCl drop wise with shaking the aqueous and ethereal layers until a light green color persists in aqueous layer. Calculations: 1- Calculate the chemical factor (each 1 ml of N/2 HCl is equivalent to 0.07205 g of S.B.). 2- Calculate the quantity of sodium benzoate in your sample. 3- Calculate the percentage w/v of your sample. Organic pharmaceutical chemistry Post-lab report third stage (HW) 1- Why we add ether in this assay? 2- Calculate the chemical factor for sodium benzoate which is equivalent to 1ml of N/2 HCl.