storage of "other" aldehydes

Alysoun

Basenotes Junkie
Feb 4, 2011
Should aldehydes other than the C-somethings be stored diluted in alcohol for better preservation? For example hexyl cinnamic aldehyde, hydroxycitronellal, veratraldehyde.
 

David Ruskin

Basenotes Dependent
May 28, 2009
As usual; depends. Some aldehydes are more reactive and prone to oxidation than others. I would dilute Benzaldehyde, Lilial and Hydroxycitronellal. Never had problems with either Hexyl Cinnamic Aldehyde or Amyl Cinnamic Aldehyde. Cinnamic Aldehyde, on the other hand, should be diluted.
 

Chris Bartlett

Basenotes Plus
Basenotes Plus
Jul 17, 2011
It certainly does depend and the solution isn't the same for all materials either. I have read that the best way to preserve Hydroxycitronellal is to add about 10-20% Hydroxycitronellol to it but as I've yet to find somewhere I can buy a reasonable amount of the alcohol I've not tried it - anyone done so? David?

Phenylacetaldehyde is often sold already let down to 85% or 50% in something else, most commonly PEA, but if you buy it pure it pays to dilute it, whether in PEA, ethanol, benzyl alcohol or whatever, otherwise it tends to polymerise.

It's worth noting that when you do this kind of dilution there is a reaction taking place (to produce hemiacetals from the aldehydes) which is quite often exothermic: so the liquid will get warm, perhaps even hot. Not significant in most circumstances but enough to mean it's worth leaving the container unsealed for a while after you mix them to avoid any pressure build up, especially if you're working on a scale larger than a few ml.

With many of these things it's also worth considering whether it's worth adding some BHT or similar antioxidant to reduce oxidation.
 

David Ruskin

Basenotes Dependent
May 28, 2009
I had forgotten about the formation of hemiacetals; so maybe ethanol is not the best solvent to use. And of course Phenylacetaldehyde should be diluted, it can get very thick as it oxidises into Phenyl Acetic Acid, or polymerises. It used to be diluted 50:50 in PEA as it was thought that the PEA acted as a quenching agent as stopped the Phenyacetaldehyde from being such a sensitiser. Citral in Limonene, and Cinnamic Aldehyde in Eugenol were also used. IFRA and other modern regs ignore this supposed "quenching".

Never heard of using Hydroxycitronellol with Hydroxycitronellal; and thinking about it I don't know if I have ever smelled the alcohol.
 

Chris Bartlett

Basenotes Plus
Basenotes Plus
Jul 17, 2011
I had forgotten about the formation of hemiacetals; so maybe ethanol is not the best solvent to use. And of course Phenylacetaldehyde should be diluted, it can get very thick as it oxidises into Phenyl Acetic Acid, or polymerises. It used to be diluted 50:50 in PEA as it was thought that the PEA acted as a quenching agent as stopped the Phenyacetaldehyde from being such a sensitiser. Citral in Limonene, and Cinnamic Aldehyde in Eugenol were also used. IFRA and other modern regs ignore this supposed "quenching".

Never heard of using Hydroxycitronellol with Hydroxycitronellal; and thinking about it I don't know if I have ever smelled the alcohol.

The quenching idea is still mentioned in my 2nd Edition copy of Curtis & Williams I think, so evidently still has some currency amongst academics even if the regulators are ignoring it.

The use of hydroxycitronellol I thought I'd read in Bedoukian and, having just checked, it's mentioned there so I expect that's where I got it from, but I too have never smelt it so perhaps that's one of those that never made it beyond the laboratory chemists. Bedoukian says this about hydroxycitronellal:
... there are certain limitations to its stability. For this reason, its dimethyl acetal is sometimes employed, although it does not have the power and character of the aldehyde. Another aromatic often used with hydroxycitronellal is its alcohol. The latter has a subdued character but blends well with the aldehyde. A small amount of the alcohol stabilizes the aldehyde, probably through hemiacetal formation.
and then later in the chapter:
Aldehydes react with alcohols to form hemiacetals which are much more stable towards oxidation. This property of hydroxycitronellal was taken advantage of in a patent12 which claims that the addition of 25% or more of hydroxycitronellol to hydroxycitronellal produces a hemiacetal which is more stable than the aldehyde alone and has a lily-of-the-valley odor. The manufacture of hydroxycitronellol and its use as a perfume fixative is described in another patent13.

12 - US Patent number 2,265,437, Dec 9, 1941
13 - US Patent number 2,258,132, Oct 7 1941
 
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Alysoun

Basenotes Junkie
Feb 4, 2011
Yes, thank you, David, Chris. I'm startled to hear I could be ignorantly producing exothermic reactions.
 

Alysoun

Basenotes Junkie
Feb 4, 2011

One of the things my safety reading emphasised was "don't mix chemicals at random". I take that to mean that I should know in advance what reactions will occur and what are the risk characteristics of the new substances, how much heat will be generated and how fast. How can I do that when I'm mixing dozens of things together? I reassured myself probably foolishly that most aroma chemicals must be fairly non-reacting, and that when Basenotes posters write that while a perfume matures, hundreds of "micro-reactions" are taking place, it's just a manner of speaking. Do regular perfumers write hundreds of equations before they mix? If not, surely this is blind folly and 'hoping for the best'.
 

David Ruskin

Basenotes Dependent
May 28, 2009
Alysoun you are quite right in that most aroma chemicals are not reactive (well not that much, anyway). However there are chemically reactive materials used, just that they are not that reactive. If there is heat generated, it isn't that much. Organic reactions take much longer than non-organic ones. I don't know of any Perfumer who has blown himself up when compounding. Mixing an aldehyde such as Hydroxycitronellal with Ethanol will, eventually result in the formation of a hemi-acetal with the production of a certain amount of heat; but no where near enough to be worried about.

There is one thing you should be careful of though. If you dip a smelling strip into neat Hydroxycitronellal or Citral and leave it for some time, quite a bit of heat will be generated, as the aldehyde is oxidised. With those two chemicals it is probably better to dip the strips into water when you have finished with them. But again, there is nothing to worry about.
 

Alysoun

Basenotes Junkie
Feb 4, 2011
David, when you say aroma chemicals are not that reactive, do you mean they don't react rapidly? I have in mind this sort of scenario, that A and B react slowly to produce C, and that when, after a year or two, C reaches a certain concentration, it catalyses a reaction between D and E to produce . . . say, a toxic gas, and when someone opens the bottle and sniffs it, she falls down dead, or has hallucinations, or something. Can I exclude that sort of thing happening if I haven't predicted the reactions in detail?

I don't think I'm likely to dip smelling strips in neat chemicals, but speaking of citral, I do sometimes put litsea cubeba neat on a tissue and fasten that to a flywire screen in the window, for air freshening. While it's in the window the heat should dissipate, yes?, but when I dispose of the tissue, sounds like I should wet it first. (And I appreciate that citral is cheaper than litsea cubeba, but I've only just started buying chemicals.)
 

David Ruskin

Basenotes Dependent
May 28, 2009
Alysoun, you are joking, aren't you? I think if a Fragrance had the potential to produce a toxic gas, someone might have noticed by now. Many aroma chemicals are chemically active; they can oxidise, polymerise, and react with other chemicals to produce such things as Schiff's Bases, esters and hemi-acetals. Sometimes these reactions are accompanied by the production of heat (an exothermic reaction), sometimes the reaction is endothermic and the whole thing gets colder. Organic reactions are usually slower than non-organic ones. Your scenario is completely without foundation.

Litsea Cubeba is about 70.0% Citral, so on a smelling strip in an enclosed space it could heat up. I doubt there is a problem the way you use it.
 

Skelly

Super Member
Jan 4, 2013
Lewisite (2-chloroethenyldichloroarsine) smells of geranium, apparently. But don't put it in your blends.

Edit: I'm just kidding here. Lewisite is a nerve agent. David is right - there is no need to worry about making anything horribly toxic. But you still need to practise good lab hygiene eg ethanol is highly flammable.

-
 

Alysoun

Basenotes Junkie
Feb 4, 2011
Alysoun, you are joking, aren't you? I think if a Fragrance had the potential to produce a toxic gas, someone might have noticed by now.
Somebody might have noticed. It doesn't follow that an amateur first beginning to blend is aware of it. And I'd rather be ridiculed here than star as the clown at my own inquest, or feature in the Darwin awards. I didn't mean to irritate you, however.
 

David Ruskin

Basenotes Dependent
May 28, 2009
You didn't irritate me Alysoun; I was just surprised at your apparent naivety. If it is lack of chemical knowledge, that can be rectified. Anyway, please do not be concerned about the potential for fragrances to produce toxic gas; it is quite difficult to do that.
 

RedX042

New member
Jun 1, 2013
Quote:


I think if a Fragrance had the potential to produce a toxic gas, someone might have noticed by now.







Well, quite a few commercial fragrances do smell like toxic gas...



:grin:


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Chris Bartlett

Basenotes Plus
Basenotes Plus
Jul 17, 2011
Quote:

Originally Posted by David Ruskin /forum/post/2959533

I had forgotten about the formation of hemiacetals; so maybe ethanol is not the best solvent to use. And of course Phenylacetaldehyde should be diluted, it can get very thick as it oxidises into Phenyl Acetic Acid, or polymerises. It used to be diluted 50:50 in PEA as it was thought that the PEA acted as a quenching agent as stopped the Phenyacetaldehyde from being such a sensitiser. Citral in Limonene, and Cinnamic Aldehyde in Eugenol were also used. IFRA and other modern regs ignore this supposed "quenching".

Never heard of using Hydroxycitronellol with Hydroxycitronellal; and thinking about it I don't know if I have ever smelled the alcohol.

The quenching idea is still mentioned in my 2nd Edition copy of Curtis & Williams I think, so evidently still has some currency amongst academics even if the regulators are ignoring it.

The use of hydroxycitronellol I thought I'd read in Bedoukian and, having just checked, it's mentioned there so I expect that's where I got it from, but I too have never smelt it so perhaps that's one of those that never made it beyond the laboratory chemists. Bedoukian says this about hydroxycitronellal:


Quote:

... there are certain limitations to its stability. For this reason, its dimethyl acetal is sometimes employed, although it does not have the power and character of the aldehyde. Another aromatic often used with hydroxycitronellal is its alcohol. The latter has a subdued character but blends well with the aldehyde. A small amount of the alcohol stabilizes the aldehyde, probably through hemiacetal formation.


and then later in the chapter:


Quote:

Aldehydes react with alcohols to form hemiacetals which are much more stable towards oxidation. This property of hydroxycitronellal was taken advantage of in a patent12 which claims that the addition of 25% or more of hydroxycitronellol to hydroxycitronellal produces a hemiacetal which is more stable than the aldehyde alone and has a lily-of-the-valley odor. The manufacture of hydroxycitronellol and its use as a perfume fixative is described in another patent13.


12 - US Patent number 2,265,437, Dec 9, 1941
13 - US Patent number 2,258,132, Oct 7 1941




After a long time looking for it I'm quite unreasonably excited to report that a sample of Hydroxycitronellol arrived here this morning! It is a clear liquid of thick syrupy consistency and mild floral odour. I'll be doing some experiments with it over then next few weeks to see how it behaves.



Oh and btw I hadn't spotted all those chemistry jokes until I came back to this today, so I'll just add a physics one:



You can't trust atoms: they make up everything!



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otocione

Super Member
Aug 30, 2011
As a chemist, I think this is the best thread I can exploit to come back to the forum after some month of standby :grin:

Always nice to read some chemistry joke :thumbup:

In-topic funfact: it is said that hydrogen cyanide (which by the way is considerably toxic) smells pretty much the same as benzaldehyde. Some of my professors years ago used to tell that when they were young, one of the ways to detect hydrogen cyanide without confusing it with benzaldehyde was to light up a cigar in the lab and pay attention to the smell of it smoke. I wasn't told what was supposed to happen but I deduced that in presence of hydrogen cyanide it probably should change drastically its odour.

Funny end note: for many people the odour threshold of hydrogen cyanide is probably higher than its lethal concentration so I always wondered if the person who first reported its smell actually survived after writing it somewhere



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pkiler

Basenotes Plus
Basenotes Plus
Dec 5, 2007
As a chemist, I think this is the best thread I can exploit to come back to the forum after some month of standby :grin:

Always nice to read some chemistry joke :thumbup:

In-topic funfact: it is said that hydrogen cyanide (which by the way is considerably toxic) smells pretty much the same as benzaldehyde. Some of my professors years ago used to tell that when they were young, one of the ways to detect hydrogen cyanide without confusing it with benzaldehyde was to light up a cigar in the lab and pay attention to the smell of it smoke. I wasn't told what was supposed to happen but I deduced that in presence of hydrogen cyanide it probably should change drastically its odour.

Funny end note: for many people the odour threshold of hydrogen cyanide is probably higher than its lethal concentration so I always wondered if the person who first reported its smell actually survived after writing it somewhere

WOW! That's some seriously twisted chemistry humor...



So I guess that the chicken crossed the road because he wanted to get to the Chem lab?



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nicok

Super Member
Aug 7, 2012
Could somebody summarize the materials that need to be diluted in alcohol in order not to become oxidized (apart from the Aldehydes)? I had some lilial neat for over a year and it started developing something like sugar crystals. It still smells wonderful but I think slightly weaker
 

David Ruskin

Basenotes Dependent
May 28, 2009
Lilial is an aldehyde, and oxidises to an acid, which is solid. As far as I am aware this acid is odourless, so your sample will become weaker over time.
 

JayH

Super Member
Sep 10, 2013
Lilial is an aldehyde. If someone has a handy list of every aromachemical prone to oxidation I will be greatly surprised. Which ones are you concerned about?

Edit: Should have hit refresh.
 

nicok

Super Member
Aug 7, 2012
I don't know. I have more than 100 materials and I knew only about aldehydes. And here I read about Hydroxycitronellal and lilial. So there are maybe more materials we should preserve in alcohol. I wonder about lyral, muguet aldehyde, Gamma-octalactone, cis jasmone.. any actually that should be preserved somehow. Chris Barlett could probably help with the additional list.
 

Graphite

Basenotes Dependent
Sep 28, 2012
I would like to revive this thread in order to resolve the question of how I should treat my chemicals.
I've pulled out more than a dozen of materials off my cardbox which I think are aldehydes (indicated by the functional o=c–h group) and I am ready to add some alcohol to prevent them from oxidizing. First big question: How much is enough?
I have no BHT here so I'd take plain ethanol. I am not sure if I want to use phenylethyl alcohol for this kind of dilution as I quite dislike its smell. Is there another concern about using ethanol except the possible occurrence of warmth while the reaction takes place?

What about the solid materials, vanillin and veratraldehyde?

Here is my list of the suspicious chemicals that have not been clarified in this thread yet:

Aphermate CAS# 25225-08-5
Citral CAS# 5392-40-5
Cyclamen aldehyde CAS# 103-95-7
Helional CAS# 1205-17-0
PADMA CAS# 100-73-2
Vanillin CAS# 121-33-5
Veratraldehyde CAS# 120-14-9


Thanks in advance!


P.S.: These were already mentioned but maybe some of you have additional information/experiences.

Cinnamyl aldehyde CAS# 104-55-2
Hexyl cinnamic aldehyde CAS# 101-86-0
Hydroxycitronellal CAS# 107-75-5
Lilial CAS# 80-54-6
Lyral CAS# 31906-04-4
Phenyl acetaldehyde CAS# 122-78-1
 

David Ruskin

Basenotes Dependent
May 28, 2009
A brief summary. Alcohols are oxidised to produce Aldehydes; which in their turn may be oxidised to produce Acids. Some Aldehydes are more prone to this oxidation than others. So to prevent this oxidation from happening the best thing to do is to protect the Aldehydes from any oxidising agent (i.e. Oxygen). Keep the bottle stoppered tightly, never keep it half empty, and ideally keep it in the dark (UV will increase the reaction rate) and in the cold. Adding Ethanol will cause the production of Acetals, it will not prevent the oxidation process. Please don't use PEA, it smells of Rose and will ruin your stuff. Vanillin and Veratraldehyde are more stable and don't need much protection; just keep them dry, cool and in a dark bottle. PADMA is not an aldehyde; PADMA stands for Phenyl Acetaldehye Dimethyl Acetal. Like most Acetals ( the reaction product of an Alcohol and an Aldehyde it is fairly stable at neutral pH). Aphermate is an Ester (the reaction product of an Alcohol and an Acid). The others in your list of "suspicious chemicals" are Aldehydes and so need to be stored with care. If you store in the cold, dry and dark, with little exposure to the atmosphere you should be OK.
 

Graphite

Basenotes Dependent
Sep 28, 2012
Thank you David, for your answer.
Somehow I knew it couldn't be that easy to spot aldehydes as an amateur.
The idea with PEA I got from the posts #3 and 4, but after rereading I understand the method of quenching an aldehyde with it's own alcohol.
Ok. So everything is fine. As long as I don't store my small bottles beside the heating or let them sunbath.
Maybe I'll experiment. Decanting some into a 5 ml bottle and fill up the half full 10 ml bottle with ethanol. Then wait and smell. Luckily the amounts I am handling and storing are still small.
 

nicok

Super Member
Aug 7, 2012
Graphite, also something that maybe interesting. Recently I dissolved aldehyde C12 lauric at 1% in perfumers alcohol (about 80-85%ethanol) to use for blending and I made a solution of 50% with the rest of it in perfumers alcohol to preserve it better.

Although I think that that wasn't enough. The 50% solution has now oxidized I guess, as it has now something like white salts.
The 1% solution has only a tiny little white salt floating around.

I guess for aldehydes particularly I should have used 96 grade ethanol and solution no more than 20%. Live and learn.

I'd also like to know from somebody experienced if I can still use the 1% solution for my fragrances, given that I haven't noticed any difference in its scent and that this white salt that has been formed is really tiny.

It's also surprising that aldehyde c8, c9, and MNA that I have in my collection are absolutely fine. I only noticed this thing first time with c12 lauric.
 

David Ruskin

Basenotes Dependent
May 28, 2009
Aldehyde C12 Lauric is particularly prone to oxidation; I don't know why. Lilial is the same. As I wrote in post 4, Phenyacetaldehyde used to be mixed 50:50 with PEA because it was thought that PEA "quenched" the sensitising effect of Phenylacetaldehyde. IFRA no longer accepts this (the same with Citral and Limonene; and Cinnamic Aldehyde and Eugenol). Mixing Phenylacetaldehyde with PEA helps a bit with oxidation, not much, and PEA is not much use with any other aldehydes.
 

nicok

Super Member
Aug 7, 2012
I haven't noticed anything to lilial though, it just becomes slightly weaker as the time goes by. Shall I preserve it in alcohol too you think David?

It's a pity that some of the most beautiful materials like lilial oxidise
 

David Ruskin

Basenotes Dependent
May 28, 2009
If it is stored badly you will notice a solid white material around the rim of the bottle of Lilial; that is the oxidation product. If you do not see this solid forming, you have nothing to worry about.
 

Graphite

Basenotes Dependent
Sep 28, 2012
Nicok, I diluted C11 enic and C12 MNA in November to 20% using 96.5% ethanol. They look fine.
 

JEBeasley

Basenotes Dependent
Jul 24, 2013
If it is stored badly you will notice a solid white material around the rim of the bottle of Lilial; that is the oxidation product. If you do not see this solid forming, you have nothing to worry about.

My Lilial had the white powder under the screw cap threads within two weeks of buying it and I keep it in a cool place... Does it normally go bad that fast? It still smells ok albeit not very pungent - it's got a light aquatic, floral smell. All of my other aldehydes from the same order are fine months later. How long do they normally last under optimal conditions? How about under sub-prime conditions?
 

David Ruskin

Basenotes Dependent
May 28, 2009
Lilial oxidises really quickly if left uncovered; that why you notice the white solid around the cap of the bottle. Usually the stuff inside should be OK for quite a while. Keep it is the cool and the dark, and it should last for at least 6 months to a year. I would check it then, and act accordingly. Most perfumery materials should be checked every 6 months to make sure they are still good.
 

Graphite

Basenotes Dependent
Sep 28, 2012
I can imagine it also depends on how it was stored before you received it. And how old it was already when you made the purchase.
 

JEBeasley

Basenotes Dependent
Jul 24, 2013
So, when an aldehyde goes bad it solidifies or forms powdery residues and/or looses it's smell? Bummer. Do all aroma chemicals eventually go bad or just aldehydes? Is there always a telltale sign that they are bad? Now I'm concerned that I have bad AC's and don't know it, hahaha.
 

David Ruskin

Basenotes Dependent
May 28, 2009
As I explained above, the group of chemicals called Alcohols can oxidise (react with Oxygen) to produce the group of chemicals called Aldehydes. In turn, Aldehydes can be oxidised to produce the group of chemicals called Acids. Some Aldehydes are more reactive than others ( in the above posts it has been shown that both Aldehyde C12 lauric and Lyral oxidise fairly quickly). Some Acids are solid, the acid derived from Lyral and from Aldehyde C12 laurie are both solid. However, not all acids are solid.

Most chemicals will react with their environment in some way, the best way to store them is to minimise this reaction. There are some aroma chemicals which are very stable, and never change; some are very reactive ad change fairly quickly. It is a good idea to store all of your materials in a cool, dark environment, and check they still smell OK every 6 months or so.
 

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