PMGB

Case 1: using potassium carbonate

A mixture of the phenol (0.001 mol), potassium carbonate (0.002 mol) and aliphatic bromide (0.001 mol) was heated at 65 ^oC for 2 h. The reaction mixture was cooled to room temperature; filtered, washed the precipitate with 10 mL acetone and the combined filtrate and washings was evaporated. The residue was diluted with 50 mL dichloromethane and washed with 50 mL water, dried (MgSO₄) and evaporated to give the O-alkylated product which was purified by silica gel column chromatography using a gradient of hexane and ethyl acetate in 65% yield.

Case 2: using cesium carbonate 

A mixture of the phenol (0.0054 mol), aliphatic bromide (0.01 mol) and cesium carbonate (0.01 mol) in 30 mL anhydrous DMF was heated at 70 ^oC for 12 h. The reaction mixture was diluted with 50 mL ethyl acetate (to precipitate out maximum dissolved cesium carbonate), filtered, washed the precipitate with ethyl acetate, the combined filtrate and washings were washed with 500 mL water (to remove DMF), dried (MgSO₄) and evaporated to give the O-alkylated product which was purified by silica gel chromatography using a gradient of hexane and ethyl acetate in 95% yield.

Case 3: selective O-alkylation of phenol in the presence of an aliphatic OH group

A mixture of the phenol containing an aliphatic OH group (0.0012 mol) and potassium carbonate (0.0012 mol) in 5 mL acetone was heated at 65 ^oC for 2 h. The reaction mixture was cooled to room temperature and added drop wise the aliphatic bromide in 5 mL acetone. The resulting mixture was stirred for overnight (12 h) at room temperature. The reaction mixture was filtered, washed the precipitate with acetone and the combined filtrate and washings was evaporated. The residue was diluted with dichloromethane and washed with water, dried (MgSO₄) and evaporated to give the O-alkylated phenol with the aliphatic OH group which was purified by silica gel column chromatography using a gradient of hexane and ethyl acetate in 97% yield.

HCl salt to free base: 

To a stirred suspension of the amine HCl salt (0.2 mol) in dichloromethane was added  aqueous solution of NaHCO₃ (0.4 mol) in 300 mL water. The mixture was stirred for 30 minutes at room temperature until it became a clear solution. The organic layer was separated, dried (Na₂SO₄) and evaporated. To recover more product from the aqueous layer it was saturated with sodium chloride, 500 mL dichloromethane was added and stirred at room temperature for overnight (12 h) to give the corresponding amine in a total of 92% yield.

Free base to HCl salt:

To a solution of the amine (0.001 mol) in 2 mL dichloromethane was added 4 mL 2M HCl solution in diethyl ether. The mixture was stirred at room temperature for 10 minutes. The solvent was evaporated, residue was triturated with ether, and solid precipitated was filtered, washed with ether and dried to give the corresponding HCl salt in 70% yield.

Another example:

Reference: US Patent 5,324,732 (a great ref. for many kind of salt preparation)