Vapor Phase Synthesis of Annelated Pyridines over Metal Modified Zeolite Beta
1–5), whereas the increase in concentration of ammonia
resulted in higher selectivity of the desired product 3a
(Table 4, entries 2, 7, 10).
The effect of WHSV on the cyclization of 1a with 2a
and NH3 was studied from 0.25 to 1 h-1 and the results are
shown in Fig. 1. The maximum selectivity of the product
3a was obtained at 0.5 h-1 WHSV. Upon further increase
in WHSV, conversion of cyclohexanone (1a) and selec-
tivity of 3a were decreased. This might be due to the less
contact time between the reactant and the catalyst.
The reaction was carried out over 1, 3, 5, 7 and 10 wt%
Pb-modified Hb zeolites and the results are shown in
Fig. 2. The 5 wt% Pb-modified Hb zeolite was found to be
more active for this cyclization reaction to form 3a. Further
increase in the wt% of Pb decreased the both catalytic
activity and selectivity. This might be due to the blocking
of active sites by excess loading.
The time on stream was studied at 350 °C and 0.5 h-1
WHSV for 10 h duration and the results are shown in
Fig. 3. The conversion of 1a and selectivity for 3a is stable
for the initial 4 h and slowly decreased with time. Deac-
tivation of the catalyst is observed over the time, this might
be because of accumulation of coke on active sites.
Fig. 4 NH3-TPD profiles: a Pbb b Hb
Table 7 Desorption of ammonia of Hb and 5 % Pbb at different
acidic regionsa
Catalysts Aciditya (mmol/g) Acidic sitesbdistribution
LT-peakc MT-peakc HT-peakc
3.3 Cyclization of Cyclohexanone with Various
Aldehydes
Hb
0.47
25.4
55.3
74.6
41.6
–
5 % Pbb 0.63
3.1
This strategy has been extended by varying the aldehyde.
Surprisingly, increase in alkyl chain length of the aldehyde,
the selectivity of corresponding 9-substituted octahy-
droacridines (3) were decreased and 6-substituted octahy-
drophenanthridines (4) were increased (Table 5). This may
be due to the restriction of the transition state by the
channels of the zeolites [27], i.e., the transition state for the
reactions that yields 9-substituted octahydroacridines were
too large to be accommodated within the pores of the
zeolites used in this reaction.
a
Total acidity amount determined by NH3-TPD
The NH3-TPD (%) distribution of acidic sites
b
c
LT-peak represents weak acid sites (150–250 °C), MT-peak rep-
resents medium acid sites (250–550 °C) and HT-peak represents
strong acid sites (550–650 °C)
Table 8 Synthesis of 1,2,3,4,5,6,7,8-octahydroacridine: Catalyst
reusability studya
Entry Cycle
TOS (h) Conversion (%)b Selectivity (%)b
3a 4a Others
3.4 Cyclization with Various Cyclic Ketones
1
2
3
a
1st use
2nd use
3rd use
1
4
1
4
1
4
94
92
95
97
93
91
88
84
85
84
86
83
7
8
9
7
5
9
5
8
6
9
9
8
This novel method for the cyclization reaction was applied
to a variety of cyclic ketones over 5 wt% Pbb catalyst. As
shown in Table 6, cyclopentanone (1b), cyclohexanone
(1a) and cycloheptanone (1c) undergo cyclization to pro-
vide the corresponding annelated pyridines in moderate to
excellent selectivities.
Cyclohexanone:Formaldehyde:Ammonia (1:1:5), 5wt% Pbb (4 g),
Temperature = 350 °C, W.H.S.V = 0.5 h-1
b
Products were quantified by GC
3.5 Temperature Programmed Desorption
of Ammonia (NH3-TPD)
optimum molar ratio of 1a, 2a and ammonia is 1:1:5. At
this molar ratio, the highest selectivity of 3a was obtained
(Table 4, entry 2). Higher concentration of 2a resulted in
lower selectivity of the desired product 3a (Table 4, entries
The TPD-NH3 profiles of Hb and 5 % Pbb catalysts are
given in Fig. 4 and the respective results of total acidity are
shown in Table 7. As can be seen from Table 7, total
123