pseudoisomethylionone by Aldol condensation of citral with methylethylketone

This experiment is a variation to this one, just a ketone with one more carbon was used and something had to be adjusted on the fly according surprises experienced:

pseudoionone by Aldol condensation of citral with acetone
https://www.sciencemadness.org/whisper/viewthread.php?tid=16...

experiment
In 1 L RBF was thoroughly mixed 205 g of rapidly magnetically stirred methylethylketone (99,7 % purity) of room temperature (it should not be ice cold, read later) with 6,33 g 40% NaOH (2,53 g NaOH + 3,8 g water). It did not fully mix with MEK unlike with acetone, solubility of water in MEK is only 10% at 20 C and much less when conc. water solution of NaOH. Then immediately 102,0 g of previously vacuum distilled citral (0,67 mol) was added while continued rapid magnetic stirring. Heating commenced and set to 40 C on heating mantle (perhaps it would be better to set to 60 C since the beginning, read later the reason, MEK does not boil at 60 C unlike acetone), the reaction was only slightly exothermic (much less than with acetone very likely due poor miscibility of conc. water solution of NaOH with MEK). When T reached 40 C, the time was started to count and continued rapid magnetic stirring (the faster the better due to poor miscibility). Mouths of flask covered with plastic sheets fixed with rubber bands to prevent air oxidation of citral. The temperature spontaneously reached peak 45 C but later fell to 40 C at which it was kept for the rest of time by the heating mantle (it would be very likely better to keep it at 60 C, read later). Meanwhile I studied more materials online and found that MEK is bound into methylene group if using HCl gas (luckily I used NaOH) and in one experiment when NaOH catalytically condensing MEK with an aldehyde obtained from alfa pinene they used even temperatures -10 to 0 C to make bond to -CH2- group. While methyl group -CH3 is bound at higher temperatures if using NaOH (in one experiement they used 60-65 C). So after 1,5 h at 40 C I decided to increase the temperature to 60 C at which the reaction was kept for another 90 minutes. This reaction is slower than with acetone due to poor miscibility of catalyst and also higher temperature favors binding methyl group.



After 90 minutes of rapid stirring at 60 C the reaction was stopped by addition of 9 g citric acid monohydrate in small amount of water while magnetically stirring (prior neutralization if stirring stopped the catalyst water solution of NaOH quickly settled at the bottom).

2-butanone distilled out at and very likely the water due to less difference in their boiling points than when using acetone. When the ketone was distilled out and still small amount of water present the distillation clearly change its typical sound into something like when you fry schnitzels on hot pan with fat/oil. Na mono/dihydrogencitrate salts appeared flying in the flask like a donut (that's why it was essential to stir during the distillation to prevent bumping and local overheating !!!)

193,6 g turbid distillate collected in receiving flask (MEK+water). After settling a little of water separated as bottom layer (almost invisible, only very small amount like 2-5 ml) and both layers become clear, water was salted out using CaCl2 to recover MEK, solubility of water in MEK 10% at 20 C.

Red crude product from distillation flask was washed 4x100 ml water in 250 ml sep. funnel, obtained 124,7 g = 0,60 mol (M=206,33 g/mol) of wet product. Dried with anh. CaCl2, 122 g = 0,59 mol of the product.

Predistilled at water aspirator level vacuum using lazy setup without condenser (just cooling directly attached receiving flask with a snow, there is a winter here now), T in distil flask approx 130 C, collected 40,3 g distillate (but you can collect less and separate forerun later at stronger vacuum level). Here most of the unreacted citral present and also few drops of water although previously drying with CaCl2. It is very good to remove all the moist / water before stronger vacuum distillation, also degassing the content to be distilled at first with weaker vacuum.

Vacuum distilled using the same 2-stage oil rotary vane vacuum pump used for citral distillation.
Collected forerun upto 112 C, cca 5 ml.
Collected main fraction b.p. 112-125 C, 52 ml.



here materials why here the temperature is better 60 C than using lower T:

https://www.journal.csj.jp/doi/10.1246/bcsj.27.131
In the condensation of benzaldehyde with methyl ethyl ketone by aqueous sodium hydroxide, the lowered reaction temperature (3∼5°) favored the aldol condensation at the α-methylene group of the ketone as in the condensation of furfural with the ketone. On the other hand, the elevated reaction temperature (60∼65°) conducted exclusively the condensation at the α-methyl group of the ketone, giving 1-phenyl-1-penten-3-one (I). 3-Methyl-4-phenyl-4-butanol-2-one (II), obtained by the aldol condensation at the lowered reaction temperature (3∼5°)

https://www.thevespiary.org/library/Files_Uploaded_by_Users/...
when aqueous NaOH was employed as the condensing agent, benzaldehyde condensed with methyl ethyl ketone at the alfa methyl group of the ketone at ordinary temperature, forming 1-phenyl-1-penten-3-one, and, when hydrogen chloride was employed as the condensating agent, benzaldehyde reacted with methyl ethyl ketone at its alfe methylene group, giving 3-methyl-4-phenyl-3-buten-2-one.
...
furfural condensed with MEK by aqeous NaOH at its methylene group at the lowered reaction temperature 0-5 C,... condensed at its alfa methyl group at 60-65 C



photos



beginning of the reaction, it looks smooth but the catalyst is poorly miscible





nonetheless the reaction proceeds, here after 15 minutes just before reaching 40 C





after 90 minutes at 40 C (note it would be very likely better to heat it to 60 C)





after 90 minutes at 60 C, almost the same color





after neutralization with excess concentrated water solution of citric acid





distilling out MEK under necessary magnetic stirring, at the end a cake of Na mono/dihydrogencitrates flying at the surface like a donut





transferred into sep. funnel to be washed with H2O




washing 4x with 100 ml water and then dried with CaCl2



[Edited on 29-11-2023 by Fery]

dry crude product going to be predistilled at water aspirator pump vacuum level





lazy setup for vacuum predistillation at water aspirator pump vacuum level (degassing, removing last traces of MEK and moist), receiving flask directly connected without messing condenser, receiving flask cooled by a snow





product in the distillation flask after removing lower boiling point contaminants





distillate collected, a lot of unreacted citral and few drops of water (weight 40 g)





full vacuum distillation using regular setup (also a condenser present)





collecting forerun, cca 5 ml (most of the unreacted citral already removed at predistillation at water aspirator pump vacuum level)





collecting main fraction 112-125 C





the product is pale yellow (very likely due to conjugated carbonyl C=O group with two C=C double bond groups)

The third one which I very likely got after cyclization in 85% H3PO4 (with linear "tail") should have much higher boiling point due to 1 carbon longer "tail". A similar effect could be observed in b.p. differences between linear n-hexane (b.p. 69 C) and branched isohexanes (b.p. 60-65 C). Here in isomethylionone / methylionone the difference >50 C seems to be like an error as the difference is just 1 carbon which changed position in 14 carbon molecule which is much smaller change than 1 positionally changed carbon in C6 (iso)hexanes.

Unfortunately I have only 5 ml of both alpha ionone and alpha methylionone which is unsuitable for distillation to measure preciously boiling points. I do not have such suitable small scale distillation apparatus and filling my smallest 50 ml flask with 5 ml sample is not good idea for precise measuring b.p. due to overheating walls of almost empty flask. Also the purity of alpha is never so good as purity of thermodymically most stable beta (it could be like 60% alpha + 20% beta + 20% gamma although according the color obtained it seems not to contain too much beta).



alpha ionone (citral + acetone -> pseudoionone -> cyclisation of pseudoionone in 85% H3PO4)





beta ionone (citral + acetone -> pseudoionone -> cyclisation of pseudoionone in 70 wt.% H2SO4 + 30 wt.% acetic acid) much more yellow / orange due to 2 conjugated C=C double bonds with carbonyl C=O group, it is easy to distinguish beta just due to its color, beta is always the most thermodynamically stable due to this conjugation, alpha as well gamma could be rearranged easily into beta by an action of conc. H2SO4





very likely alpha methylionone (citral + butanone (cat. NaOH, elevated temperature) -> very likely pseudomethylionone -> cyclisation of pseudomethylionone in 85% H3PO4) so this is a cyclization product from the compound dedicated to this thread





I wonder whether the branched variant, that's "pseudoisomethylionone is obtained at very low temperatures around 0 C using hydroxide catalyst. Because here they claim that it requires hydroxide + high temperatures
https://www.chemicalbook.com/ChemicalProductProperty_EN_CB51...

Quote: Originally posted by Fery

No way how to assess the purity.