Prelab for the Synthesis of a Merocyanine Dye
John Stephenson, 410-1306
Prepared for Allyson Campbell
Organic Chemistry II
Introduction
A synthetic merocyanine dye with unusual properties is prepared in this lab. MOED,
formally named 1-methyl-4-[(oxocyclohexadienylidene)ethylidene]-1,4-dihydropyridine
is a maroon solid who’s colour in solution is dependent on the polarity of the solvent that
it is dissolved in. The synthesis starts from 4-methylpyridine and through a simple SN2
alkylation reaction with methyl iodide, 1,4-dimethylpyridinium iodide is formed. This
carbon nucleophile is then reacted with 4-hydroxybenzaldehyde, a carbon electrophile. A
carbon-carbon double bond is formed and 4-(4-hydroxystyryl)-1-methylpyridinium
iodide is produced. Finally deprotonation of this species results in the maroon solid,
MOED. This reaction from starting materials to MOED is shown in Scheme 1.
Scheme 1: The formation of MOED
I
CH3 I
+N
O
+
CH3
CH3
H3C N
OHH3C N
C
H
C
H
O
+
OH
H C
I
+
H3C N
C
H
C
H
OH
Outline
Step 1: Outline for 1,4-dimethylpyridinium iodide
- Add 3mL isopropanol and 1.5mL 4-methylpyridine to a 50mL r.b flask
- Set up for reflux, add 0.93mL methyl iodide, swirl flask
- Warm the flask to 50 and remove from heat source
- Remover from heat, an exothermic reaction will happen
- Allow the mixture to stand for 15 minutes
- Suction filter product, washing with isopropanol, suction dry
Step 2: Outline for 4-(4-hydroxystyryl)-1-methylpyridinium iodide
- Add 1.8g 1,4-dimethylpyridinium iodide, 0.91g 4-hydroxybenzaldehyde, 15mL 1propanol and 0.75mL piperidine to a 25mL r.b. flask
- Reflux on a steam bath for 45 minutes
- After 45 minutes, cool flask in an ice-bath
- Suction filter product, washing with methanol, suction dry
- Recrystallize from methanol (7.5mL per 0.1g). Recrystallization occurs slowly.
Step 3: Outline for MOED
- Add 1.5g 4-(4-hydroxystyryl)-1-methylpyridinium iodide to 0.25g in 75mL water in a
125mL Erlenmeyer flask
- Heat the mixture on a steam bath until the solid dissolves, then cool
- Allow to stand overnight, collect crystals by suction filtration, wash with water.
- Characterize by UV, 1H NMR
Table of Products
Name
Formula
M.W. (g/mol)
1,4-dimethyl
pyridinium iodide
C7H10NI
235.07 g/mol
Theoretical
Yield
(g, mmol)
3.53g
15mmol
4-(4-hydroxystyryl)-1methylpyridinium
iodide
C14H14NIO
339.17 g/mol
2.54g
7.5mmol
(1-methyl-4-[(oxocyclohexadienylidene)ethyl
idene]-1,4-dihydro
pyridine)
C14H13NO
211.27 g/mol
0.951g
4.5mmol
Actual
Yield
(g, mmol)
Percent Yield
(%)
Table of Reagents and Solvents
Name,
Formula
4-methylpyridine
C6H7N
Methyl iodide
CH3I
1,4-dimethylpyridinium
iodide
C7H10NI
4-hydroxybenzaldehyde
HO(C6H4)CHO
Piperidine
C5H11N
4-(4-hydroxystyryl)-1methylpyridinium iodide
C14H14NIO
Potassium hydroxide
KOH
1-methyl-4-[(oxocyclohexadienylidene)ethylid
ene]-1,4-dihydropyridine
C14H13NO
1-propanol
CH3CH2CH2OH
Isopropanol
CH3CHOHCH3
Methanol
CH3OH
Acetone
CH3COCH3
Water
H2O
M.W.,
m.p/b.p (C),
density
93.13 g/mol
mp 2.4, bp 145
d15 0.957
141.94 g/mol
mp –66.5, bp 42.5
d20 2.28
235.07 g/mol
(solid at 25)
Hazards
Amount
Mol ratio
Flammable
Poisonous
1.5mL, 1.39g
15mmol
1 equiv
0.93mL, 2.11g
15mmol
1 equiv
1.8g
7.5mmol
1 equiv
0.91g
7.5mmol
1 equiv
0.75mL, 0.65g
7.5mmol
1 equiv
1.5g
4.5mmol
1 equiv
0.25g
4.5mmol
1 equiv
~20mg (x4)
Poisonous
Volatile
122.12.g/mol
mp 116
85.15 g/mol
mp –12, bp 106
d20 0.8622
339.17 g/mol
(solid at 25)
Strongly basic
56.11 g/mol
mp 380
Corrosive
211.27 g/mol
(solid at 25)
60.10 g/mol
bp 97.2, mp –127
60.10 g/mol
bp 82.5, mp -88.5
32.04 g/mol
bp 64.7, mp -97.8
58.08 g/mol
bp 56.5, mp -94
18.02 g/mol
bp 100, mp 0
Flammable
Poisonous
Flammable
Poisonous
Flammable
Poisonous
Flammable
Poisonous
Drowning
hazard
Solvent
Solvent
Solvent
Solvent
Solvent