DISCUSSION AND RESULTS

DISCUSSION AND RESULTS

3.1) Observations

When the mixture of thiamin, water and EtOH was cooled down, a white

precipitate was formed.

The final product is almost pearly white and “spiky” crystals.

Its fusion temperature is 134.7‐136.2 °C which is in agreement with the values

given by the protocol: 134‐136 °C.

3.2) Yield

molar mass [g/mol] n th [mmol] n exp

[mmol] yield [%]

212.24 196 44.1 23%

9.3679g of product were obtained after recrystallization. This represents a 23%

yield. The protocol said that the mass should be 10g (48%) but actually 10g

represent 24% of yield (taking benzaldehyde as the limiting reagent). So the

result is satisfying.

4. SPECTROMETRY DATA

4.1) NMR 1H (CDCl3, 400MHz)

bond shift ∂ [ppm] multiplicity hydrogen

C‐H 7.92 multiplet benzene H1

C‐H 7.55‐7.27 multiplet benzene H2, H3, H5, H6, H7

C‐H 5.97 doublet H4

O‐H 4.57 doublet H8

O

O

H2

H1

H3

H2

H1

H4

H5

H5

H6

H6

H7

H8

δ 7.92 (m, 2H) ; δ 7.55‐7.27 (m, 8H); δ 5.97 (d, J=6.0 Hz, 1H); δ 4.57 (d, 6.0 Hz, 1H)

There is a problem with the multiplet corresponding to δ 7.55‐7.27 ppm because

the integral should show only 8 hydrogens, but atually shows 9. The problem

could be the solvent (CDCl3) that would have been left in the product.

4.2) IR (neat, cm‐1)

3404; 1679; 1263; 1204; 1092; 1068; 977; 753; 696; 673

We can clearly see major peaks: one at 3404 cm‐1, corresponding to the O‐H

stretch and another at 1679 cm‐1, corresponding to the C=O stretch of an

aldehyde.

Therefore the IR confirms that it is the expected product.

5. QUESTIONS

1) What is the thiamine formula and what is its action mechanism in the reaction

of benzoin condensation?

See “mechanism”. Thiamine is a catalyst; it is regenerated each time a benzoin

molecule is synthesized.

2) Show how cyanide can replace thiamine in this reaction.

OH

S

N+

NH2 N

N

Cl-

3-((4-amino-2-methylpyrimidin-5-yl)methyl)-5-(2-hydroxyethyl)-4-

methylthiazol-3-ium chloride

It is the same mechanism as the one with thiamine. So cyanide can also be

used as a catalyzer. [3]

3) The pyruvate decarboxylase is an enzyme depending on the thiamine which

catalyses the decarboxylation of pyruvic acid to acetaldehyde. Write a

mechanism for this transformation and note down the bibliographic reference.

The mechanism is an oxidative decarboxylation, with a release of CO2.[4]

6. REFERENCES

H

O

N C

H

...