Take phthalimide convert it into its K salt on treatment with KOH then react with alkyl halide to form N-alkyl phthalimide & hydrolyse to get amine. Procedure is available in Text book of practical Organic Chemistry by A.I.Vogel.

These large peaks may be due to contamination of  solvent ether .Akyl groups from amines will also exhibit the PMR signals depending upon alkyl chain because of spin-spin coupling.

I would agree with Madhukar about the solvent being contaminated, so perhaps try a different one if you can. I had success using refluxing hydrazine hydrate (30mins) to remove a phthalamide from a protected sulfonamide, but I didn't use NaOH at all, and I extracted with ethyl acetate.

Take phthalimide convert it into its K salt on treatment with KOH then react with alkyl halide to form N-alkyl phthalimide & hydrolyse to get amine. Procedure is available in Text book of practical Organic Chemistry by A.I.Vogel.

Dear Thinh,

Could you give us some more details: the structure of the starting alkyl bromide, perhaps a scan of the 1H NMR spectrum of the resulting reaction mixture...? It is difficult to help you with the data you have provided to us now...

agree with Niko, more details are needed to get some possible reason

Try this modified Gabriel Synthesis,  Attached.

Use refluxing hydrazine hydrate for the deprotection step, avoid NaOH. The intramolecular transamidation to form the phthalazine byproduct doesn't require base, and you may be getting partial hydrolysis to form the acid amide. We'd need to know the monomer to give any further help.

The phthalazine byproduct can also be very difficult to remove and may be the source of your strange peaks. If you are specifically looking for NH2 in 1H NMR spectra, make sure you are using very dry deuterated solvents as solvent exchange can cause N-H peaks to appear diminished.

Thinh, can you please compare your reaction process with the mechanism in the attached file?

Check this also.

Put here your reaction scheme. Gabriel synthesis usually does not fail

A very nice way is to use sodium diformyl amide with the alkyl bromide ; hydrolysis with HCl Very efficient !

agree with Teodoro. More detail about your reaction is needed!

 Bernard has a very good idea, but it might happen that you might be short of money, and you can use the classic method only.

 From your description it might be concluded that the removal of the phthalic group was not complete. Try to boil for a longer time first.

 For the phthalic method, I would recommend you to "isolate" first the amine salt. Although, the removal of phthalhydrazide is (technically) not easy, but it might be more effective.

1. remove HH as much as possible by rotavap if your amine is not volatile. - If it is volatile, you may try (fractioned) distillation (up to C7-8 amine, depending on your technical availabilities), too, either from the reaction mixture.

2. add HCl to get acidic solution (in water)

3. filter the solids

4. Add cc. ammonia to make the solution basic. If your primary amine is not soluble in water and it is solid, then you can filter it, if not you can extract your product. But, perhaps it is better to use other org. solvent than Et2O.

 Alternatively, you may convert your primary alkylbromide to azide and reduce it by transfer hydrogenation, depending on the properties (Pd/C and HCOOH, HCOONH4, or HH).

Thanks all for your helpful advices,

My initial monomer has Naphthalene ring and alkylbromide in its structure. I let it react with excess amount of potassium phthalimide in DMF solvent and heat for 8 hours and then extract with cloroform and NaOH solution, water. The NMR spectra shows the peak of phthalimide attach to my initial monomer at 8ppm, the other peaks still remain, but some shifts occur. I think attaching phthalimide is successful.

And then, excess amount of Hydrazine react with this phthalimide coumpound in THF at 80C for 4hours. Solvent is removed and the solid remained was stir with 20% NaOH solution. Then extract with ether and water. There is strange peak at the alkyl region with high intensity and the peak of phthalimide disappears. In my opinion, if there is by-product of phthalimide, the H-NMR peak should be in the region over 5ppm. However, the strange peaks are in 1 - 4 ppm region, I don't think these are phthalimide by-product.

And the reason why I didn't use HCl is my monomer has a big structure and highly hydrophobic, so that it could form precipitate when treat with HCl solution. Hence, I can't seperate it with phthalimide. Is it right?

You can see my NMR spectra below

0.88 and 1.2 are grease, a common impurity. 3.46 might be diethyl ether with the other signal obscured by the grease peak. I can also see some DCM. If I had to blame anything It looks like the hydrazine has reacted with THF as the peaks are consistent with NH2NHCH2CH2CH2CH2OH. Hard to be certain if the phthalyl impurities are gone without looking at integrals but it doesn't look like any remains.

You probably do have your product but it is very impure, try to purify your compound. Test your THF for peroxides and run the reaction again with a different solvent; toluene perhaps.

 I don't agree with Laszlo for the expensive process. You need only MeONa  30 % solution in MeOH and formamide. You mix  the reagents in a bubble flask and evaporate MeOH by heating  with the rotary evaporator at atmospheric pressure. You can produce 500 grams of the salt in 1 hour.

Some procedure show only sodium hydroxide used without hydrazine after reaction with pottasium phthalimide with alkyl halide. Do anyone try that procedure?...In my case Intermediate yield is too low.

Some procedure show only sodium hydroxide used without hydrazine after reaction with pottasium phthalimide with alkyl halide. Do anyone try that procedure?...In my case Intermediate yield is too low.