To answer your questions, It would be useful to know your starting material for this Vilsmeier-Haack reaction. Also, if you need to reach pH 14 do not use sodium bicarbonate.

Thanks Philippe Roger Bovy , my starting material is (acetanilide).

shodhganga.inflibnet.ac.in/jspui/bitstream/10603/78768/20/20_chapter-13.pdf

Don't fixate on the colour: while the increasing yellow tint can be connected to the formation of your product, it's too unspecific to be used as measure of the progress of your reaction. You can use TLCs as reaction control, for instance.

Basification is important. Your product is basic and your reaction forms copious amounts of HCl as byproduct. You will get protonation of your product to the corresponding quinolinium salt. Basification yields you your free product. And yes, as mentioned you will need NaOH.

The crushed ice hydrolyses the intermediate from the Vilsmeier-Haack reaction as well as the remainders of the Vilsmeier reagent and the POCl3, so you will need at least enough for that task. Ten times the (volume?) amount of the DMF is absolutely enough, but you could probably get by with less.

For purification, I would try recrystallisation first. If that does not give a pure enough product, try column chromatography.

For basification, there is good to use NaHCO3 and lead the solution to pH 6-7, not to 14. Strong base area leads to obtaining by-products, such as products of Cannizzaro reaction. Go to the neutral solution, in this case the yield of the product will be optimal.

The condition you have used is little bit harsh and can lead to side products specially the formation of 2-hydroxy-3-formylquinolin, as the chlorine is susceptible for nucleophilic substitution in strong alkaline medium. You can follow the following procedure and I think you can get better yield and quality. To the required amount dry DMF (excess to be taken as it is solvent cum reagent) taken in a two neck r.b. flask and cooled to 0-5 degree centigrade, POCl3 (about 3-4 equivalent was added drop wise with stirring and the stirring was continued at 0-5 degree centigrade for about 20 minutes protecting from moisture (Anhyd. CaCl2 guard tube can be used). Now to it a solution of acetanilide in dry DMF was added drop wise. The reaction mixture was allowed to attain r.t gradually with stirring. It was then heated at 60-70 degree centigrade for 5-6 hours. Completion of the reaction was checked by TLC (if not completed it is to be stirred with heating for a longer time). The reaction mixture was then cooled to r.t and then poured into crushed ice with vigorous stirring. Saturated NaOAc solution was added to the mixture with vigorous until pH reached to 5-6. The stirring is continued for 15-20 minutes further. The product formed is filtered (if solid) or extracted with ether or DCM. Washed thoroughly with NaHCO3 solution and then with ice water and dried under vacuum (if extracted, product can be obtained after removal of ether or DCM) . The crude product can then be purified either by re-crystallization from suitable solvent or by column chromatography. Hope you will get the desired 2-chloro-3-formylquinoline in pure form. (Prior to use POCl3 to be purified by distillation from little P2O5 for better results)

Thanks Prof. Gandhi K. Kar for your support. I tried your procedure and it was helpful but generally the yield is low and it takes a long time. i found after long search the following method using Sodium Dodecayl Sulfate (SDS) as miceller media:

A Vilsmeier Haack adduct prepared from POCl 3 (9.3 ml, 100 mmol) and DMF (7.7 ml, 100 mmol) at - 5 ° C was slowly added to a solution of 4-Br- acetanilide ( 1j ) (1.070 gr, 50 mmole) in acetonitrile containing a solution of SDS (10ml of 0.05 mol) in acetonitrile and refluxed for 45 min. After completion of reaction, as indicated by TLC, the acetonitrile was evaporated and the reaction mixture was dissolved in CH2Cl2 and quenched with sodium thiosulphate solution. The organic layer was separated, dried over Na2SO4 and evaporated under vacuum, purified with column chroma-tography using ethylacetate:hexane (3:7) as eluent to get the pure product 6-bromo-2-chloro-3-formyl quinoline ( 2j ) in 90% yield

I tried to dissolve SDS pellets (50 mmole) in acetonitrile (1L) but it didn't dissolve.

How can i prepare SDS solution ?

Dear Ayman Mohamed Ibrahim

Thank you for your query. One of my student did the reaction (as said by him and he is now working elsewhere) and he told me that he got good yield. If you need, I can ask him for details of the procedure. In fact to reduce the time and to increase the yield you can heat it at 60-70 degree as a trial method. You can increase the amount of POCl3 and DMF too. I have not done the reaction in my lab before.

Any way,  to dissolve SDS first of all you crush the pellets into powder form and the try to dissolve in acetonitrile or DMF. It's solubility may be less.......in that case to dissolve, it may need sonication. since I have not used it, I can only predict but I have no practical experience. But you can try.

Thanking you

Prof. Gandhi K. Kar