Lab Report for “Synthesis of Benzoic Acid”
Complete questions 1-6 in the experimental section of this laboratory procedure.
1) Write an equation which describes the reaction which has occurred.
2) What would the Grignard Reagent be converted into if water accidentally got into the flask?
3) How does the 1,2-dibromoethane serve to initiate the reaction of the magnesium with the
bromobenzene?
4) Write an equation which describes what occurs when the phenylmagnesium bromide is added
to the dry ice.
5) Using an equation, show what reaction occurs when the H2SO4 is added to the carbonated
reaction mixture.
6) Using a flow diagram, show what occurs in this washing/extraction procedure through the
addition of the 6 M HCl.
7) Determine the percentage yield of benzoic acid. Include in your calculations a BALANCED
EQUATION and the following information:
a.
b.
c.
d.
e.
number of moles of reactants used;
the limiting reagent in the reaction;
theoretical yield of benzoic acid obtainable
the actual yield of benzoic acid obtained
the percentage yield.
8) Give the m.p. of the benzoic acid you prepared and the literature value.
9) Analyze the IR spectrum of benzoic acid which you obtained in the laboratory. In the
Spectral Report Form, identify:
a. the -OH absorption
b. the C=O absorption
c. absorptions characteristic of an aromatic ring
10) Analyze the 1H and 13C NMR spectra of benzoic acid which appears on the next page, and
fill out the Spectra Report Form. Pay particular attention to the acidic hydrogen (COOH) 1H
NMR signal (is there one? why not?)
11) Analyze the mass spectrum of benzoic acid specifically answering the following:
a. Give the structures of the cations responsible for the m/e 77, 105, and 122 signals.
(Hint: what is the m/z for the molecular ion?)
b. What is the relationship between the m/e 105 and 122 signals; the m/e 51 and 77
signals?
12) Analyze the mass spectrum of bromobenzene specifically answering the following:
a. The molecular weight of bromobenzene is 157 amu. Explain the appearance of the
m/e 156 and 158 signals of about equal intensity.
b. Suggest a structure for the cation responsible for the m/e 77 signal.