Benzaldehit-Metil Alkol tepkime kinetigi asidik formdaki katyon degistirici
reçine (Amberlit IR-120) varlıgında çalısıldı. Çözücü olarak 1,4-dioksan kullanıldı.
Bir denge tepkimesi olan asetal olusumunun, hidrolizine oranla yavas olması
nedeniyle, ileri tepkime olarak hidroliz tepkimesi çalısıldı. Benzaldehit dimetilasetalin
hidrolizine ait denge sabiti 298-328 K sıcaklık aralıgında
Kd= exp(8,67-1880/T)
olarak bulundu. Burada T, Kelvin olarak mutlak sıcaklıktır.
Amberlit IR-120 katalizör varlıgında gerçeklestirilen deneyler sonucunda,
hidroliz tepkimesinin adsorplanmıs su molekülleri ile yıgın içindeki asetal molekülleri
arasında gerçeklestigi (Eley-Rideal modeli) ve tepkimenin “yüzey tepkimesi basamagı
kontrollü” oldugu gösterildi. Tepkime hızının ise;
2
( )
1
BA M
A W
e
W
BA BA W W
m C C
k C C
V K
r
K C K C
−
− =
+ +
seklinde verilebilecegi bulundu. Burada derisimler mol L-1’dir. Asetal hidrolizi
yönündeki hız sabitinin sıcaklıga baglı olarak
k = exp(9,4- 4915/T) L2 ( g-kuru reçine) -1.mol -1.dakika -1
esitliginden hesaplanabilecegi gösterildi. Benzaldehit ve suya ait adsorpsiyon denge
sabitleri ise
KBA = exp (7292/T-24,9) L.mol-1
KW = exp(1296/T-4,4) L.mol-1
seklinde bulundu.
The kinetics of acetalisation of benzaldehyde with methyl alcohol has been
studied in the presence of a cation exchanger in its acidic form (Amberlite IR-120). 1,4-
Dioxane has been used as solvent.
Acetalisation is an equilibrium reaction, and it was found that the rate of acetal
formation is much slower than that of acetal hydrolysis. Hence hydrolysis, rather than
acetal formation, was choosen as forward reaction. In the temperature range 298-328 K,
the equilibrium constant for hydrolysis of benzaldehyde dimethyl acetal was found to be
Kd= exp(8,67-1880/T)
Where, T is absolute temperature in Kelvin.
In the presence of catalyst, the reaction has been found to be occured between an
adsorbed water molecule and a molecule of acetal in the bulk phase (Eley-Rideal
model). From this model it was concluded that the reaction is “surface reaction control”
and its rate will be given by expression
2
( )
1
BA M
A W
e
W
BA BA W W
m C C
k C C
V K
r
K C K C
−
− =
+ +
Where, concentration are in the unit of mol L-1. It was shown that temperaure
dependency of hydrolysis rate constant can be given by
k = exp(9,4- 4915/T) L2 ( g-dry resin) -1.mol -1.minute -1
The adsorption equilibrium constants related to benzaldehyde and water were
also calculated to be
KBA = exp (7292/T-24,9) L.mol-1
KW = exp(1296/T-4,4) L.mol-1
respectively.
