I am trying to use n-butyl group as nucleophile to synthesise linear chain based secondary alcohol.
BuLi is not the best choice!
In your case I would prefer the classical
Grignard reaction
If its is must that n-BuLi is to be used, consider reaction in presence of diethyl ether as solvent at -78 Celsius under argon conditions. THF can also be used. To quench it try saturated aq NH4Cl solution.
Use flame dried solvent and dry degassed THF under nitrogen or argon. Cool it to -78 degrees and add 1.2 equivalents of the commercially available BuLi hexanes solution. Add your aldehyde/ketone as a solution in THF to the BuLi. The ratio of solvent volumes should 1:1:1 for THF : BuLi hexanes : aldehyde/ketone in THF. Allow it to reach room temperature then quench under nitrogen with saturated aqueous ammonium chloride.
The first lot of THF breaks up the BuLi aggregates in solution and makes the reaction much faster. Adding the aldehyde/ketone as a solution in THF helps prevent it from freezing. If it still isn't behaving then you can try adding a few equivalents of tetramethylethylenediamine.
The Grignard is a good alternative and is commercially available, or can be prepared in the usual fashion from butylbromide. If you are preparing the grignard then you may as well try the one-pot Barbier conditions. The aldehyde/ketone, the alkyl bromide and Mg or Zn in THF, heated at a rate to maintain reflux. You may need to activate your Zn or Mg first, depending on its quality.
Further alternative route for this preparation is via the so-called "Umpolung" !! See literature!
In a second step you have to reduce the ketone to obtain the secondary alcohol.
Therefore, you take your carbonyl compound (aldehyde) and condense it with ethylene- dimercaptane. Then remove the acidic proton from the cyclic acetal and proceed with nucleophilic displacement using eg butylbromide. Finally, remove the thio-component under oxidative conditions according to well described literature. Then reduction with eg NaBH4 is the final step. Good luck!
n-BuLi is not the best option, in this case you must work at -78C under Ar atm using Et2O or THF as solvent. If you only want to add an alkyl chain and form the secondary alcohol, your best option is a Grignard reagent, commercially or labmade using Mg and the bromide of the desired alkyl chain (see literature)
If you premix CeCl3 (anhydrous) and nBuLi then slowly add electrophile to that mixture at -78, you'll get very good yield of the alcohol. I know it sounds strange, but check out Tsuneo Imamoto. I have applied his method to much more complicated substrates and nucleophiles. Cerium trichloride is a cool one.
Pure & Applied Chemistry 1990 Vol. 62 pp. 747-752.
Chem. Rev. 2010, 110, 6104-6143.
Butyllithium will show two properties as a base and neucleofile where grignard will show only nuecleophilic character and very minute basic character.so,Grignard is the best reagent.