Preparation of TriH(ethynyl)benzene (DEPROTECTION METHOD)

Tri(TMS)ethynylbenzene ---------------> Tri(H)ethynylbenzene
NaOH
DCM/MeOH

1. starting material are dissolved in DCM
2. NaOH are dissolved in MeOH (*refer calculation given)
3. mix 1 and 2

*mass of NaOH = (mol of starting mat. x JMR NaOH)4

PURIFICATION STEPS

• take the reaction mixture to dryness
• dissolve the residue in DCM, wash with small amout of water
• the two layers obtained are separated in a separatory funnel
• dry the organic phase layer over MgSo4
• then, filter it using filter paper
• the volume was reduced to ~10 ml
• the product was then purified using column chromatography (follow the previous purification steps for Tri(TMS)ethynylbenzene)
• the collected orange and yellow band are subjected to rotavapor
• NMR characterization

NOTES!!

Percentage yield obtained was 114% which indicates that the product obtained contains impurities.

It might resulted from unefficiency skills of separation (trace amount of catalyst and foreign matter may still remain).

NMR proves that some peaks due to grease and at 3.797ppm (still not sure due to what compound) are present.

However, NMR clearly shows that the product obtained is the true compound.

Preparation of Trimethylsilane(TMS)ethynylbenzene

TriBrbenzene -----> TMS(ethynyl)benzene

TMSA
Pd(PPh3)2Cl2
CuI
Et3N

ref: Uhl,W.,et.al, Organometallics, 2007, 26, 2363-2369

• starting material + Et3N are placed in RBF


• apparatus are purged with vacuum, then followed by N2


• repeat purging for at least 3x to ensure no air remain in the system
  
• add Pd(PPh3)2Cl2 and CuI in the closed system


• add excess of TMSA, (refer the calculation given)

ml of TMSA = (mol of tribromobenzene x JMR TMSA x 1/density of TMSA)

• all the steps above are performed at RT


• next, mixture are heated to ~60 degrees for almost 7 hours.

MAKE SURE!!

• water tap is open during the heating for enabling the condensation to occur effectively


• put clips on joints so that none of the Et3N solvent (which are very very volatile) get evaporated, thus leaving the mixture in dry (which was exactly my mistake!)


• attach the upper part of condenser to N2 bubbler and the lower part to vacuum to make sure no moisture (from the condensation) get into the mixture


• never ever do your 1st trial at large scale, you should familiarise yourself with the methods and skills first since some of the chemicals used are quite expensive (such as Pd(PPh3)2Cl2)


• always and should never forget to close the system before adding Pd(PPh3)2Cl2 catalyst since air can actually 'kill' your catalyst (here goes your precious catalyst)

PURIFICATION STEPS

1. let the mixture to cool down


2. the mixture is the filtered off using vacuum suction to get rid of the salt


3. wash with diethyl ether


4. residue is put to rotavap and take it to dryness


5. n-pentane is added to dissolve the solid residue after rotavap


6. purication steps are then performed in column chromatography;

• almost a beaker of Al2O3 is added into column chromatography
• the Al2O3 powder need to be wetted evenly with 5%ethyl acetate/ petroleum spirit
• transfer the mixture from RBF by using pasteur pipette with extra care (do it alongside of the column to reduce the Al2O3 bed disturbance)
• carefully add 5%ethyl acetate/petroleum spirit to separate the band
• collect the desired band (dark yellowish)
• rotavap the collected solution to dryness and vacuum it to reduce all the moisture
• NMR charaterization

Percentage yield obtained = 97%