chemrox
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preparation of cinnamic acid from benzaldehyde
I have nearly pure benzaldehyde in the form of oil of bitter almond. Could I use this without purification to make cinnamic acid via (?) http://www.prepchem.com/synthesis-of-cinnamic-acid/
which would then be distilled to get rid of unreacted aldehyde and other volatiles.
aldehyde, volatiles not in dictionary !!?!
"When you let the dumbasses vote you end up with populism followed by autocracy and getting back is a bitch." Plato (sort of)
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zed
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I don't trust such materials to actually be pure, or even to contain benzaldehyde. Oh, it's a such a wicked world! So personally, I would probably
try to isolate/purify the benzaldehyde (if any) before pulling the trigger.
Though I must admit, the temptation would be strong, to try the quick and dirty approach.
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tshirtdr1
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Cinnamic Acid
For this reaction, you are getting an aldol addition, then elimination to form an alpha, beta unsaturated product. I agree that you need to distill
your benzaldehyde first. If you want to try this for fun, then go for it. We do a similar reaction in lab with acetone and benzaldehyde which gives
dibenzalacetone (a fluffy yellow product) in high yield. If you are doing this just for fun, you might try that one.
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Loptr
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I was going to recommend purifying the adduct, but I will just pull the entry from Purification of Laboratory Chemicals.
Benzaldehyde [100-52-7] M 106.1, f - 2 6o, b 6 2o 5 8o/10mm, 1 7 9 . 0o/760mm, d 20 1.044, n 20 4D
1.5455, pK25 -7.1 (aqueous H2SO4). To diminish its rate of oxidation, benzaldehyde usually contains additives such as hydroquinone or catechol. It can
be purified via its bisulfite addition compound but usually distillation (under nitrogen at reduced pressure) is sufficient. Prior to distillation it
is washed with NaOH or 10% Na2CO3 (until no more CO2 is evolved), then with saturated Na2SO3 and H2O, followed by drying with CaSO4, MgSO4 or CaCl2.
[Beilstein 7 IV 505.]
[Edited on 9-4-2016 by Loptr]
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Dr.Bob
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Most benzaldehyde contains a good amount of benzoic acid from the air oxidation of the aldehyde, so the wash with base is very helpful, as it removes
a large amount of the acid. Once distilled, the material will start oxidizing immediately if not kept under inert gas, so try to limit the amount of
air it is in contact with. Storing it in a nearly full bottle is best, to minimize any air in the headspace. Purification would be a good idea for
any aldehyde, unless the reaction is not bothered by the acid. For instance, in some reductive aminations, you can just use an excess of the
aldehyde, and the acid does not interfere much. But for many other reactions, the acid contamination is quite detrimental, such as any type of strong
base chemistry.
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chemrox
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Quote: Originally posted by Loptr  | I was going to recommend purifying the adduct, but I will just pull the entry from Purification of Laboratory Chemicals.
Benzaldehyde [100-52-7] M 106.1, f - 2 6o, b 6 2o 5 8o/10mm, 1 7 9 . 0o/760mm, d 20 1.044, n 20 4D
1.5455, pK25 -7.1 (aqueous H2SO4). To diminish its rate of oxidation, benzaldehyde usually contains additives such as hydroquinone or catechol. It can
be purified via its bisulfite addition compound but usually distillation (under nitrogen at reduced pressure) is sufficient. Prior to distillation it
is washed with NaOH or 10% Na2CO3 (until no more CO2 is evolved), then with saturated Na2SO3 and H2O, followed by drying with CaSO4, MgSO4 or CaCl2.
[Beilstein 7 IV 505.]
[Edited on 9-4-2016 by Loptr] |
I read that too. Since it was obtained years ago as the volatile oil it should be free of additives but not free of other volatile oils. That said for
all I know "pure" volatile oils may have other "natural" materials to stabilize them. I don't know much about this industry. There might be other
aldehydes that would make some minor co-products.
[Edited on 12-4-2016 by chemrox]
"When you let the dumbasses vote you end up with populism followed by autocracy and getting back is a bitch." Plato (sort of)
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Loptr
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I have had 250mL of benzaldehyde stored as the adduct for a while now. I haven't had a need for it, but it looks just as it did the day I filtered it
from the solution.
I don't know how much you have on hand, simply because you mentioned in another thread that you have more piperonal than you will ever need (???), so
you might have hundreds of gallons for all I know. However, personally, if it is of an unknown quality I would vacuum distill, use what you need
immediately, and prepare the adduct from the rest. The adduct is storage stable from my experience.
All of this you know already, so I am preaching to the choir.
[Edited on 12-4-2016 by Loptr]
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UC235
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| Quote: Originally posted by zed | I don't trust such materials to actually be pure, or even to contain benzaldehyde. Oh, it's a such a wicked world! So personally, I would probably
try to isolate/purify the benzaldehyde (if any) before pulling the trigger.
Though I must admit, the temptation would be strong, to try the quick and dirty approach. |
Essential Oil of bitter almond should be about 95-99% benzaldehyde assuming:
1) it's the real thing and wasn't "fragrance oil" purchased by accident (a smell test will be immediately revealing if you know what pure benzaldehyde
smells like)
2) the seller does some modicum of product testing to detect adulteration. Low-effort adulteration is often done with an odorless, low-viscosity
material like (2-ethylhexyl) palmitate. In the case of oil of bitter almond, synthetic Benzaldehyde is also an option. One would need to examine C13
abundance using mass spec in order to determine if the product was derived from atmospheric CO2 or petrochemical stock. Or, one could look at the
expected amounts of other minor constituents. For chemistry, who cares about synthetic benzaldhyde.
I would also like to note that actual rectified bitter almond oil is stupid expensive so there is a huge motivation to adulterate it in some way.
Since I buy essential oils for soapmaking, I checked my various suppliers. Only one carries it and it's $424/8oz, which is about half the price of
rose absolute.
The assay on it, though, is 99.3% benzaldehyde, 0.5% benzoic acid, 0.1% benzyl alcohol, and a trace of cinnamaldehyde. That's reagent grade for all
I'm concerned.
[Edited on 12-4-2016 by UC235]
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CaptainPike
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thank you for this. It only tends to prove the old adage: "if something seems too good to be true, it probably is".
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chemrox
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| Quote: | | 99.3% benzaldehyde, 0.5% benzoic acid, 0.1% benzyl alcohol, and a trace of cinnamaldehyde. |
looks like it can be used out of the can.
[Edited on 12-4-2016 by chemrox]
"When you let the dumbasses vote you end up with populism followed by autocracy and getting back is a bitch." Plato (sort of)
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Dr.Bob
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Having recently run an NMR on a sample of a brand new bottle of a substituted benzaldehyde from a large chemical vendor, it was not even 90% pure at
the start, so that would be great. I once did a analytical study on some related chemicals, and most of the aldehyde reagents were less than 90%
pure by GS-MS, many were below 50%, but some were pretty old. But in general aldehydes don't store well.
For other geeks in the crowd, we tested a number of chemicals used for synthesis and primary amines also did not keep well in general, far worse than
I imagined in some cases. But most acids, alcohols, phenols, and even anilines were pretty stable to long storage. The amines appeared to have
some redox type chemistry, where they would oxidize to imines, which would form aldehydes, then react with the original amine to form secondary
amines. The problem was worst in halogenated benzyl amines. Or maybe they were just impure from the start, not really sure. But few reagents were
as clean as they claimed on the label, even the new bottles. That was not too surprising.
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Loptr
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| Quote: Originally posted by Dr.Bob | Having recently run an NMR on a sample of a brand new bottle of a substituted benzaldehyde from a large chemical vendor, it was not even 90% pure at
the start, so that would be great. I once did a analytical study on some related chemicals, and most of the aldehyde reagents were less than 90%
pure by GS-MS, many were below 50%, but some were pretty old. But in general aldehydes don't store well.
For other geeks in the crowd, we tested a number of chemicals used for synthesis and primary amines also did not keep well in general, far worse than
I imagined in some cases. But most acids, alcohols, phenols, and even anilines were pretty stable to long storage. The amines appeared to have
some redox type chemistry, where they would oxidize to imines, which would form aldehydes, then react with the original amine to form secondary
amines. The problem was worst in halogenated benzyl amines. Or maybe they were just impure from the start, not really sure. But few reagents were
as clean as they claimed on the label, even the new bottles. That was not too surprising. |
Thank you, Dr.Bob.
That was very interesting. What do you consider long term storage?
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Dr.Bob
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We have bottles of chemicals from days old to 30+ years old at work. So for many chemicals, long term means decades. But for aldehydes even a few
weeks is long term. But once you use up the oxygen in the bottle, the oxidation will slow down, assuming the cap does not leak too much, so the main
issue is opening the bottle, and letting air in. If you blow N2 or Ar into the bottle before resealing it, or keep it sealed with a septa and
syringe the material out under N2, that helps a lot, but nothing will be perfect, even our best efforts for catalysts does not preclude all air
infiltration.
But for most non-reactive chemicals I have found that years of storage is OK. For air or water reactives like acid chlorides, isocyanates, aldehydes,
and organometallics, even one or two exposures to air can destroy them within days to months. Some are better than others, but many are not stable
for long. And for intermediate ones, like amines, alkyl carboxylic acids, and anilines, many are stable for years, but if they have points of
oxidation, they might not last very long, like double bonds, benzylic amines, or electron rich anilines. They can go faster. Para-hydroxyaniline is
a good example, it turns dark within hours of distilling. And both of our bottles of benzoyl chloride in the lab have crusts of benzoic acid on the
caps, which make them hard to open.
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