الفهرس 
INTRODUCTIONOnly 14 pages are availabe for public view
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Abstract
The local type of lemongrass oil was obtained by stem distillation of the vegetative organs of lemongr~ss plant and the following lines represent a brief summary of the data collected during the course of the present
1. The physical and chemical characteristics of lemongrass oil include the values : specific gravity at
25°C. 0.8922, refractive index at 20°C., 1.4975, specific rotation of the oil was - 0.74, specific rotation in ethyl
-0.75 respectively, acid number 4.3, ester number before acetylation 35.4 and the ester number after acetylation (Guenther’s procedure) 216 and the carbonyl content of lemongrass oil was 75 % as determined by the hydraxylamine method.
than that in the ~~lvents isopropanol and ethyl acetate by 8%. The linear relationship between the concentration and
the corresponding observed rotation in a particular solvent definitely indicates that the change in concentration in the range 5 to 77 % , does not lead to any form of association
between the oil or some of its constituents ~nd the
The increase in specific rotation in chloro-
form over that in the solvents isopropanol and ethyl acetate could be traced to some interplay between tEe solvent molecules and the optically active constituents of the oil, such an interplay takes place in dilute and concentrated solutions to the same extent as evidenced
from the constancy in specific rotation of all solutions of the oil in chloroform between 5 and 70 %.
3. Solubility: The solubility of lemongrass oil
was carried out according to Guenther’s procedure, the oil
was clearly soluble in 1.3 volumes of 95 % ethanol, one vo lume SO % ethanol, 0.2. volume 80 % ethanol an.d. i. t ’Nas insoluble in 70 % ethanol.
~he mutual solubility of lemongrass oil in organic solvents indicated the following :
a) Preliminary ex.periments showed that lemongrass oil was
completely miscible with chloroform at room temperature in all possible concentrations, and there was no sign of turoidity at low temperatures down to -10°C. On the other hand, ethanol 95 % and isopropanol 95 % proved to be SUi~3~lp for such a study.
b) On using ethanol 95 %, it was clear that the concenttration over 55.2 % lemongrass oil gave solutions which were completely soluble, on cooling to - 10°C., the solution showed no signs of turbidity. On the other hand, lower concentrations in the range 42.47 % to 0.46 % were turbid at room temperature and required a high temperature to reach the miscibility point. The critical solution temperature of lemongrass oil was
+ 96°C. corresponding with the critical solution conncentration 8.7 % .
c) In case of isopropanol 95% , concentrations of lemonngrass oil over 39 % were completely soluble in 95% isopropanol, and did not show any signs of turbidity
on cooling to -10°C. On the other hand lower concent··r&~ions ranging between 24.48 % and 4.95 % gave turbid mixtures at room temperature and required slightly higher temperatures to attain miscibility. The critical solution temperature of lemongrass oil in isopropanol 95 % was + 54°C. corresponding with 8.08 % for the critical solution concentration.
4. The determination of the saponification number of lemongrass oil indicated the following :-
a) The use of thymolphthalein and carbon tetrachloride
as a modification to determine accurately the end point9 proved to be quite satisfactory as a substitute for the standard procedure where phenolphthalein was employed.
b) Saponification for one hour at 100°C.9 is qUite sufficcient to complete hydrolysis of the ester constituents
of the oil. Saponification was conducted at room temperature 9 60°C.9 70°C.9 and 80°C. to avoid volatility of the ester constituents which would be originally
present in the oil or formed due to transesterification. The esrer number was low at room Jemperature9 while it did not change in the temperature range between 600C. and 100°0.9 which could mean that the ester constituents of lemongrass oil are very fast in their reaction with alcoholic KOB at 60°C.
c) A series of experiments were carried out using three
different concentrations of alcoholic KOH 0.5036 N., 1.2341 N., cri 2.2386 N. for different periods and temperatures i.e. room temperature 9 60°C’9 and ~000Cw The ester value at 60°C. was higher than that at 1000C. in the latter part of the reaction which seems to indj~~~ that Cannizzaro reaction took place on prolonged heattng
at 60°C. and not at 100°C. for shorter periods or at least not to the same extent. In other words, the one hour period noted in the standard procedure is quite sufficient for the hydrolysis of the ester constituents
of lemongrass oil. Prolonged heating and more concentrated alkali solutions enhance the side reactions namely Cannizzaro reaction. Thus it is apparent that under normal reaction conditions the hydrolysis of esters takes place, while abnormal conditions favour both the hydrolysis of esters and the side reactions involving the aldehydic constituents of Egyptian lomongrass oil. The aldehyde content of 18mongrass oil
i.e. citral, represents 75 % of the oil.
d) The standard saponification procedure was applied to pure authentic benzaldehyde. The ester number turned out to be 43.0 although the value expected theoretically should be zero which indicates that some alkali was consumed by the aldehyde.
e) The use of alcoholic KOH 0.1515 N., 0.5166 N., 0.9872 N., 1.4760 N., and 2.0598 N. lead in one hour at room temperrature to the consumption of benzaldehyde to the extent
of 15 % , 22 % , 37 % , 56 % , and 73 % , and the values increase after 20 hours to 18 % , 57 % , 73 % , 88 % , and 97 % respectively.
The extent of the reaction after one hour at 60°C.
w~s ne~rly 20 % , 36 % , 63 % , 84 % and 92 % on using tLe concentra-v-:--ons C).lSlS ”., C).SloE, ~., C).~t~n2. ~., l.4-7E,O ~.
and 2.0598 N. respectively. The maximum ester number
249 + 2 representing 94 % reaction was obtained after 40 hours on using KOH 0.9872 N., in case of KOH 1.4760 N. the maximum value 258 ~ 3 representing 97.3 % reaction was reached after 5 hours. On the other hand, the maximum ester number 265 + 5 representing 100 % reaction was reached after 5 hours in case of 2.0598 N.
At 75°C., the saponification reaction takes place to the extent 20.8 % , 44 % , 72 % ? 83 % and 95 % after
one hour in the presence of the above mentioned concentrations respectively. The maximum ester value 248 + 3 referring to 94 % reaction, 258 ~ 4 representing 97.3 % reaction, 265 ~ 5 representing 100 % reaction; were obtained after 25 hours,
5 hours, 5 hours in case of KOH 0.9872 N., 1.4760 N., and 2.0598 N. respectively.
The extent of the reaction after one hour at 100°C. was 55 % , 71 % , 94 % , 96 % , and 99 % on using the above mentioned KOH concentrations respectively. The series of experiments which were conducted on the behavior of benz811dehyde during saponification lead to the conc11.Jsion +’os.t in
the case of lemongrass oil~ the increase in the ester
value noted on using different concentrations of alcoholic KOB is unquestionably due to Cannizzaro reaction. In case of Egyptian lemongrass oil~ there was no significant differrence in the ester values obtained on using KOB 0.5036 N., and 1.2341 N., although the rate of reaction was much faster with high concentrations. Benzaldehyde gave on treatment with 0.1515 N., and 5166 N. KOB the same maximum values for the ester number.
The increase in the ester value in case of lemongrass oil at 60°C.is due to subsidiary reactions between the alkali and one or more of lemongrass oil components.
f) The ester number of pure citral turned out to be 30.3 although the expected value should be zero theoretically. It ~s quite obvious that some base was consumed by the aldehyde. It is ~ well known fact that Cannizarrization of citral involves two molecules leading to the formation of geraniol and geranic acid which consumes some of the alcoholic KOP expressed in the calculation as an ester and in fact the ester value throws some light on the degree or extent of cannizzaro reaction on citral. So~ citral was heated with three different concentrations of alcoholic KOB for different periods and different temper atures. At room temperature, on using KOB 0.5036 N. and
1.2341, similar results were obtained although the rate of Cannizarrization of citral was much faster with high conncentrations. On the other hand, the increase in the percentage of reacting citral represents 10.2 % on using KOH 2.2386 N., the ester value remained constant on proolonging the reaction period.
The ester number after 40 hours at room temperature on using KOH 0.5036 N. and 2.2386 N. was similar to that
at 60°C. after 15 hours, while the ester number after 15 hours at room temperature on using KOH 1.2341 N. was similar to that at 60°C. and 100°C. after 5 hours. In addition the ester number after one hour at 60°C. r~d 100°C. on using KOH 2.2386 N. was similar to that at room temperature after 15 hours.
On carrying the reaction at 60°C. for one hour, the ester number was approximately the same as that at 100°C. on using the three different concentrations of KOR, while on increasing the reaction time at 60°C. higher values were obtained.
So, it is logical to state that the increase in the ester number at 60°C., when the Egyptian lemongrass oil was heated for long periods of time is due to Cannizzaro reaction
5. The acetylation of lemongrass oil was carried
out with the use of various acetylating agents under differrent reaction conditionsand the following points could be deduced:
a) The acetylation reaction took place very rapidly in the first few minutes. The ester number of lemongrass oil before acetylation was 35 ~ 1 and reached the value 219 after acetylation for 10 minutes and 243 after 20 minutes. The increase in the ester number due to acetylation is taken generally as an indication of the total alcohols present in the oil. However, lemongrass oil is known
to be poor in its alcoholic const cuents (1.5 %) and
rich in its aldehyde content (75 % as citral), and subbsequently it was strange that the ester number due to acetylation should reach such a high value corresponding with 57 % total alcohols. The role of aldehydes in the esterification process was examined using benaldehyde,
the ester number after acetylation of benzaldehyde was 324, 380 and 380 after 1, 3 and 50 hours which represent 86 %, 100.3 ~ and 100.3 % reaction respectively. This experiment leads to the conclusion that acetylation of aldehydes leads to the form~tion of acids by some conndensation reaction, the acid formed plays a significant
role in consuming alkali due to neutralization and actually the ester value is not a true expression in such a case.
On comparing the results of Egypti~n lemongrass oil with the results indicating the behavior of benzaldehyde, it seems logical to assume that the higher ester value of the acetylated oil is due to citral. An experiment was .conducted on the acetylation of citral, the results indi-
cated in a definite manner the possibility of condensation between citral and acetic anhydride and such a statement is supported by previous work on this specific reaction. The ester number of lemongrass acetate decreased with the increase in heating time and such a gradual decrease could be interpreted in terms of decomposition due to prolonged heating.
b) The ester number increased gradually during the course of acetylation with acetic anhydride-sodium acetate at 100°C. and reached the value 260 ~ 1 after 50 hours. The ester number remained practically constant during the heating period from 50 to 75 hours. The acetylated product was Jptically inactive.
c) At 80°C., using the same acetylating agent, the ester number reached the maximum value 260 ~ 2 after 170 hours
corresponding with the value noted after 50 hours at 100°C. The ester number remained practically constant during the heating period from 170 to 360 hours.
d) Acetylation took place very slowly at room temperature using the same reaction mixture. The specific optical rotation was quite low, i.e. -0.52 and -0.45 after one and 12 hours, while the acetylated product obtained on prolonging the acetylation period up to 12 hours was optically inactive.
e) Acetylation with glacial acetic acid at room temperature for 48 hours gave a product simi~ar in the ester value
of the original oil before acetylation. On prolonging the acetylation period, the ester number increased
was obtained after 120 days at room temperature. The specific optical rotation was low i.e. -0.63 after acetylation for one day, while on prolonging the acetyllation period, the acetylated product was optically
f) The ester number of the acetylated product using glacial acetic acid at 80°C., showed a regular and steady in-
The ester number of the acetylated product
reached the maximum value 81 ~ 2 after 50 hours at 80°C., and it remained practically constant on proolonging the acetylation period from 50 to 150 hours at 80°C. The specific optical rotation was -0.73 for the acetylated product obtained after one hour at 80°C., while the acetylated product obtained on proolonging the acetylation period was optically inactive.
g) The acetylation of lemongrass oil with glacial acetic acid was carried out at 100°C. The reaction showed a steady increase and reached the maximum ester value 85 ~ 1 after 10 hours at 100°C.
h) The ester number of the acetylated product obtained after one hour at reflux temperature with glacial acetic acid started with 74 and reached the maximum value 85 ~ 1 after 6 hours.
i) Acetylation of lemongrass oil by the alkoxide method gave different values for the ester number and the high values could be explained on the basis of the fact that the hydrogen evolved from the reaction is partially GODsumed in the reduction of citral. So, the ester number does not represent a true value of the alcohols originally present in the oil. Thus, it seems advisable to refer to the impracticability of the alkoxide method.
6. Formylation of lemongrass oil : Formic acid seems to be the most widely employed formylating agent and the following lines refer to the formylation proocedures performed in the present investigation.
a) The formylated product by Glichitch method showed
that the ester number increased gradually a.Yld steac.i.ly in the first 10 days, which indicated that the three days period specified by the standard procedure was not enough to complete the reaction. On prolonging the formylation period a significant decrease in the ester value was observed due to the possible partial decomposition of the formate.
b) The hot formylation method leads to dehydration to some extent of the alcoholic constituents of lemonngrass oil into alkenes and thus it is evident that
hot formylation would be expected to give a formylated product with a lower ester number which ranged between 52 and 69.
7. Benzoylation The use of benzoylating agent,
benzoyl chloride in pyridine proved that benzoylation is mild incomparis0u with acetylation. The ester number of lemongrass benzoate was 72 + 1 which is lower than the ester value of the corresponding acetate. The resulting benzoates had no effect on plane polarized light.
8. Isolation of citral: There are many procedures which were carried out in that direction with the object of isolating pure citral from Egyptian lemongrass oil. The two successful methods which have been used in the present work for the isolation of pure citral in lemongrass oil were the bisulfite and the neutral sulfite methods. Both
ci tral was 95 % and revealed the following average values: specific gravity at 20°C. 0.8987, refractive index at 20°C. 1.4880, the acid number 3.1 and zero for specific optical rotation.
9. The residual lemongrass oil after ci tral separation c~ntained 15 % aldehyde, it was treated again with excess sodium bisulfite to isolate the residual aldehyde, but the trial seems to be unsuccessful because the aldehyde content was again 15 %~ the residual oil gave the following constants: specific gravity at 25°0. was 0.8730, refr3c~~:~ index at 25°C. ~.4900~ the specific optical rotation was -1·58 at 25°C., acid number 2.2, ester number 43.6 and after acetylation 115.