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Alkylation of 1,4-Dimethoxybenzene

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Introduction

Alkylation of 1,4-Dimethoxybenzene Matt Steiner 11/7/2007 Introduction: The purpose of this experiment is to synthesize a tetrasubstituted benzene derivative. This will be done by using 1,4-dimethoxybenzene, 2-methyl-2-propanol (a tertiary alcohol), and sulfuric acid (H2SO4). This produces a tert-butyl carbocation electrophile because it is very easy to make since it is tertiary. The delocalized cationic intermediate corresponds to 2 resonance structures. Under the reaction conditions, there will be 2.4 moles of tert-butyl alcohol for 1 mole of 1,4-dimethoxybenzene. Since the alcohol is mildly activating and is in excess amounts, the resulting product will end up resulting in di-alkylation. When the two electrophilic substitutions occur, a tetrasubstituted product forms. Since the tert-butyl group is quite bulky this can affect which product forms. The substitution pattern on the benzene ring of the product can be determined by whether it turned out to be a liquid or solid. ...read more.

Middle

The flask was warmed on a hot plat to dissolve the solid and then cooled in an ice bath. Ice-cold concentrated sulfuric acid (1 ml) was added drop-wise to the flask with a Pasteur pipet for 1 min. The flask was cooled for 5 more minutes and then warmed to room temp for 10 minutes. 5 ml of ice cold water was added to the flask and was placed in the ice bath to try to form a solid. Since the product separated into a liquid, the procedure for a liquid product was used. 2 ml of diethyl ether was added to the reaction flask and then the contents were transferred to a centrifuge tube for extraction. After rinsing the flask with 2 ml of ether and adding the rinse to the tube, the lower aqueous phase was extracted into a 250 ml beaker. ...read more.

Conclusion

The peak at 6.8 ppm indicated the hydrogens on the benzene ring. All three methyls on both tert-butyls do not have the same proton coupling. The product does not show symmetry so the two methoxy groups are not magnetically equivalent, making two peaks. The other two peaks at around 3.4ppm and 3.8ppm are related to the hydrogens attached to the oxygens. Discussion: The yield came to be very good. No problems occurred during the experiment. Since the product turned out to be a liquid the tert-butyl groups ended up in the 2,6 position on the benzene ring. This doesn't make a line of symmetry and so does not make each methoxy groups identical. There were two separate singlet peaks showing on the NMR indicating the methoxy groups. The tert-butyl groups are very bulky and should have had an effect on the dialkylation reaction. The 2,6-tert-butyl isomer was formed because it had three large groups right next to each other and steric hindrance in the transition state did not affect its formation. ...read more.

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