Laboratory Synthesis Of PROPRANOLOL

SYNTHESIS OF PROPRANOLOL

AIM

To synthesis and find out the percentage yield of Propranolol

REFERENCES

1. Kaiser, C., Jen, T., Garvey, E., Bowen, W.D. (1997). Journal of Medicinal Chemistry, 20(5), 687-9.

2. Crowther, A.F. & Smith, L.H. (1968). Journal of Medicinal Chemistry, 11, 1009-13.

3. Jaggers, S. E.; Jones, G. (1978). Journal of Medicinal Chemistry, v. 21, n. 2, p. 182-188.

PRINCIPLE
Propranolol is the most useful nonselective adrenergic antagonist (β1, β2- blocker). Propranolol is used in the treatment of angina and hypertension. By antagonizing the β2-receptor, propranolol possesses serious problems to asthmatic patients. Propranolol presents an aryloxypropanolamine structure and has been synthesized in two steps from α-naphthol, using the route shown below:

EXPERIMENTAL
A. Synthesis of epoxide
Transfer 1.25 g (0.0085 mol) of 1-naphthol (PM = 144.18 g/mol), 0.5 g KOH to a round-bottom flask and add ethanol/H2O (9:1). After dissolution, add drop wise 4ml (0.049 moles) of epichlorhydrin (MM = 92.5 g/mol, d = 1.180 g/ml, and e.p. 114 °C). The reaction is left under magnetic stirring at room temperature for 48 h. TLC is carried out in an eluent system (hexane/ethyl acetate 9:1) to monitor the end of the reaction. Remove ethanol by vacuum evaporator. Extract aqueous phase with ethyl ether. The ethyl ether extract is dried with anhydrous sodium sulfate. Filter and remove solvent to obtain the crude brown oil. 

B. Synthesis of propranolol

Transfer 0.2 g (1.0 mmol) of the crude oil with methanol to a round-bottom flask fitted with a stopper and add 4ml of isopropylamine (47 mmol; 2.78 g; d = 0.694 g/ml). Keep the reaction under temperature control (t = 40 °C), for 2 h. Remove solvents by vacuum evaporator. To the obtained product, add 30ml of 2.0 mol/L HCl and transfer to a separating funnel. Extract with ethyl ether. Transfer the aqueous extract to an Erlenmeyer flask and alkalinize with 32ml, 2.0 mol/L NaOH, in an ice bath (0 °C), with vigorous stirring to precipitate the product. Filter the precipitate, dry in a vacuum desiccator, and recrystallize from petrol ether (boiling point = 65–110 °C). Weigh the solid.

OBSERVATION AND CALCULATIONS

Molecular weight of 1- Naphthol = 144.17g

Molecular weight of propranolol = 259.3 g

Theoretical yield = 2.25 g

Practical yield = ……… g

Percentage yield =

A white powder. M.p. 163° to 164° (crystals from n–propanol).
SOLUBILITY
Soluble 1 in 20 of water and ethanol; slightly soluble in chloroform; practically insoluble in ether, benzene, and ethyl acetate

RESULTS

At least two products are obtained in the first step reaction; however, it is not necessary to purify the crude oil. The by-product results from nucleophilic attack of potassium salt of 1-naphthol to the formed epoxide. This by-product is removed in the second step by ether extraction. The yield is satisfactory. Spectrometric data analysis is recommended.

Disclaimer: This document is provided to the general public as a courtesy; any individual, institution, or organization who choose to use this document, either in its original or in a modified form, do so at their own risk, author is not liable for injuries or accidents that occur in any lab.

 PROPRANOLOL

MW: 259.35 MF: C16H21NO2
PROPRANOLOL LD50: 28.1 mg/kg (M, i.v.); 289 mg/kg (M, p.o.);23 mg/kg (R, i.v.); 660 mg/kg (R, p.o.)
CN: 1- [(1- methyl ethyl )amino]- 3- (1- naphthalenyl oxy)- 2- propanol
PROPRANOLOL hydrochloride
MW: 295.81 MF: C16H21NO2 · HCl
PROPRANOLOL hydrochloride LD50: 18 mg/kg (M, i.v.); 320 mg/kg (M, p.o.);21 mg/kg (R, i.v.); 466 mg/kg (R, p.o.)

 Reference(s):
US 3 337 628 (ICI; 22.8.1967; GB-prior. 23.11.1962).
GB 994 918 (ICI; appl. 23.11.1962; valid from 28.10.1963).
GB 995 800 (ICI; appl. 23.11.1962; valid from 28.10.1963).

Colour Tests.

Mandelin's Test—green; Marquis Test—green.

Thin–layer Chromatography.

System TA—Rf 50; system TB—Rf 06; system TC—Rf 10; system TE—Rf 49; system TL—Rf 07; system TAE—Rf 21; system TAF—Rf 79; system TAJ—Rf 00; system TAK—Rf 05; system TAL—Rf 49. (Acidified iodoplatinate solution, positive.)

Gas Chromatography.

System GA—propranolol RI 2147, M (1–naphthol-) RI 1505, M (desamino-OH-) RI 2065; system GB—propranolol RI 2234, M (4-OH-) RI 2546, M (1–naphthol-) RI 1534.

High Performance Liquid Chromatography.

System HA—propranolol k 1.3, 4–hydroxypropranolol k 1.1; system HX—RI 377; system HY—RI 299; system HZ—Retention time 3.7 min; system HAA—Retention time 13.1 min; system HAM—not detected; system HAV—k 2.3; system HAX—Retention time 9.2 min; system HAY—Retention time 4.9 min.

Ultraviolet Spectrum.

Aqueous acid—288 (A¹₁=222 a), 305, 319; methanol—290 (A¹₁=240 a), 306 (A¹₁=143 a), 319 nm (A¹₁=86 a). No alkaline shift.

Bioavailability.

10 to 50% (mean 30).

Half–life.

Plasma half–life, 3 to 6 h (dose–dependent elimination has been reported).

Volume of distribution.

About 4 L/kg.

Clearance.

Plasma clearance, about 10 to 20 mL/min/kg.

Distribution in blood.

Plasma : whole blood ratio, about 1.3.

Protein binding.

In plasma, about 90%

Reference

Clarke's Analysis of Drugs and Poisons