AJKOER
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Interesting Chloroform Preparation from Citric Acid
Actually, before I get credit for a new (and perhaps even better) path to CHCl3, let me confess it was an accident.
My actual intent was to perform one of my previous described Hypochlorous battery cell reactions. The steps are prepare HOCl from a weak acid plus
Chlorine bleach (see so-called 'bleach battery' discussed in a prior Sciencemadness thread at http://www.sciencemadness.org/talk/viewthread.php?tid=24318 ). Add to the bleach and weak acid, pieces of Cu, Al and finally some NaCl for a good
electrolyte. The reaction normally forms Chlorine gas and salts of Aluminum and Copper. Related electrochemical references: http://www.exo.net/~pauld/saltwater/ , http://sci-toys.com/scitoys/scitoys/echem/batteries/batterie... and also http://www.dtic.mil/dtic/tr/fulltext/u2/d019917.pdf .
So, what went so wrong (or, is it right)? I decided to use, for the first time, Citric acid as the weak acid to react with NaOCl. However, per this
source, the action of HOCl on Citric acid in the presence of Copper, can form CHCl3. To quote from "Copper catalysis in chloroform formation during
water chlorination", link: https://engineering.purdue.edu/CE/Academics/Groups/Environme... per the extract:
"Copper is known to catalyze a number of reactions that are similar to the conventional haloform reaction"
and per page 4387:
"Copper used in these experiments was added in the form of copper (II) sulfate (CuSO4 5H2O, Baker, reagent grade). Sodium hypochlorite (Aldrich,
>5% available chlorine) was used as the source of chlorine. "
and most relevant per page 4391:
"The graphical summaries of chloroform formation
dynamics illustrated in Figs. 6 and 7 suggest the
existence of two (or more) steps in the formation of
CHCl3 from the chlorination of aqueous solutions of
citric acid. The reactions that occurred during the long
idle period that preceded the appearance of chloroform,
at pH other than neutral, were assumed to represent the
first step. For example, in Fig. 7 it is evident that
detectable quantities of chloroform were formed at pH 7
within 30–60 min, whereas at pH 5 and 9, chloroform
detection was delayed for several hours. Larson and
Rockwell [1] identified the first step in this sequence to
be an oxidative decarboxylation reaction."
Within 60 minutes, I also was able (by smell) to detect CHCl3.
My calculations were based on the equation:
NaOCl+46H2O + C6H8O7 ---> NaC6H7O7 + HOCl + 46 H2O
The bleach was 8.25% NaOCl by weight (1 mole with water weighs 901.81 grams) and I dissolved the appropriate amount of Citric acid mono-hydrate
(molecular weight 210.14 grams) in 20 cc of distilled water before adding it to the bleach (note, foaming does occur).
Those actually interested in producing Chloroform may wish to repeat this experiment.
[Edited on 27-11-2013 by AJKOER]
Edit by Texium: changed title to reflect more realistic expectations
[Edited on 5-18-2018 by Texium (zts16)]
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bfesser
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What calculations? So, the only thing you're telling us is that you could smell chloroform in your mixture?
[Edited on 27.11.13 by bfesser]
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Oscilllator
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So did you actually manage to isolate any chloroform? It seems that this reaction could be useful for those that cannot obtain acetone, however I
think acetone + bleach will remain the reaction of choice because of the cost of the citric acid etc.
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AJKOER
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bfesser:
I have since added more calculation details (well, at least of my intended reaction on the preparation of Hypochlorous acid, not the actual reaction
chain, which I claim only limited knowledge and understanding per the cited reference).
------------------------------
Oscillator:
I did not isolate CHCl3, only likely observed its formation, which triggered some research on what the h happened. Those interested in Chloroform
actual preparation, try this route, and please comment further. I may have need of CHCl3 at some time in the future.
As a word of caution, the fumes are quite noticeable and after a few inhalations, I started to feel something. This was not likely wishful thinking on
my part as I do not know exactly what I had formed, so beware.
On your cost comment, prior to this experiment, I happen to see an ad for Citric acid at bulk prices. I was considering buying more at $23.99 for 8
pounds (I did not get to the shipping costs), but such pricing may make Citric acid competitive with other paths depending on yield.
[Edited on 27-11-2013 by AJKOER]
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chemrox
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So, let's see, what makes this an easy CHCl3 preparation is that someone will take pity and post a legit preparation...
"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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AJKOER
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Chemrox:
My motives in posting this possible path to CHCl3 were two fold. First, it may indeed be an easy path to a newly restricted compound. And second, as
you noted, someone who has prepared this compound via other routes may be able to comment on its potential merit and provide further details on
extraction, etc., all for those interested and in need of this particular compound.
So for those interested in Chloroform, this post may get the interest of some.
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The_Davster
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What scale was this done on? CHCl3 is pretty insoluble so if it forms in appreciable amounts it should form a separate, lower, layer.
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crazyboy
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Why did you find it necessary to acidify the sodium hypochlorite, or to add copper for that matter? The haloform reaction takes place under basic
conditions, and sodium hypochlorite is generally stabilized with sodium hydroxide. It is quite trivial to make chloroform from acetone and pool
chlorine but it is not particularly economical.
The yields without copper and weak acids are near enough to quantitative, adding the other reagents won't increase available chlorine so I fail to see
how it could be of benefit.
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AJKOER
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Because I was, as I explained, I was pursuing a very different reaction. The electric producing battery cell I described provides a gentle
chlorination tool. The basic cell runs on Hypochlorous acid (in the presence of Cu, Al and an electrolyte, NaCl) which can be prepared by adding a
weak acid (like Vinegar, or a very dilute mineral acid) to aqueous Sodium hypochlorite. As a side note, do not dismiss the potential role of a
chloride salt as it has been noted in the literature as enhancing the activity of HOCl (for example, in chlorate formation). Reference: "Effect of
Chloride Ion on the Kinetics and Mechanism of the Reaction between Chlorite Ion and Hypochlorous Acid" link: http://www.researchgate.net/publication/23141635_Effect_of_c...
Quote: Originally posted by crazyboy  | | ... The haloform reaction takes place under basic conditions, and sodium hypochlorite is generally stabilized with sodium hydroxide...
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Here is some of the author's comment with respect to pH and copper per page 4393:
"Observations from the experiments with copper
support the hypothesis that copper catalyzes the
oxidative decarboxylation of citrate. The formation of
b-ketoglutaric acid is believed to be the rate-limiting step
in the formation of chloroform. Because of this step, there was a lag period in the production of chloroform
at pH 5 where the citric acid was not in the appropriate
form (the trianion of citrate). The presence of copper
reduced this lag period to 1 or 2 h instead of 3 or 4. At
neutral pH, the addition of copper to the solution
resulted in an immediate increase in CHCl3 production
rate. The presence of copper was also important at pH 9.
No CHCl3 formation was observed during the first
hours when the experiments were conducted without
copper. The addition of copper significantly reduced the
non-chloroform production period.
The observed effects of pH and copper concentration
on chloroform formation suggested that the presence of
citrate as a dianion or a trianion was beneficial for
catalysis. Copper-citrate complexation will be enhanced
by conditions that favor ionization of the three
carboxylic groups of citric acid. At pH 5, where the
majority of citric acid (62%) is in the form of the
dianion, a high concentration of chlorine (15 mg/L as
Cl2), along with the presence of copper, resulted in a
CHCl3 yield of almost 500 mg/L (4.210 6M); this
yield was 4.6 times greater than without copper. For
comparison, the initial citric acid concentration was
4.210 6M. This high degree of reactant conversion
suggests that copper may also interact with the dianion
form of citric acid for CHCl3 formation (Fig. 6b). On
the other hand, at pH 9, where most of citrate was in the
trianionic form, the relative increases in CHCl3 yield and
formation rate were greater, thereby suggesting that the
trianion is the preferred form for copper catalysis"
| Quote: Originally posted by crazyboy | ... It is quite trivial to make chloroform from acetone and pool chlorine but it is not particularly economical.
The yields without copper and weak acids are near enough to quantitative, adding the other reagents won't increase available chlorine so I fail to see
how it could be of benefit. |
I thank you for this general comparative statement. Also, access (and continued access) to pool chlorine compounds is required for the trivial path.
[Edited on 27-11-2013 by AJKOER]
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Nicodem
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| Quote: Originally posted by AJKOER | Actually, before I get credit for a new (and perhaps even better) path to CHCl3, let me confess it was an accident.
|
How can something old be new? And how can it be better, if you found it to be non-preparative?
| Quote: Originally posted by crazyboy | | Why did you find it necessary to acidify the sodium hypochlorite, or to add copper for that matter? The haloform reaction takes place under basic
conditions, and sodium hypochlorite is generally stabilized with sodium hydroxide. |
The decaboxylative oxidation of citric acid, as the oxidation of any alcohol with hypochorites, proceeds faster under moderatly acidic conditions,
because the first step involves the O-chlorination. With the Cu-catalysis the mechanism can change, and the acidic media might not be as necessary any
more. Besides, unlike in the C-trichlorination of acetone, the perchlorination of acetonedicarboxylic acid does not require basic media. It can work
under acidic media as well, to give perchloroacetone or pentachloroacetone (instead of 1,1,1-trichloroacetone as it occurs to acetone in basic media).
If you check its structure, you can easily understand why. Nevertheless, the final cleavage may require basic media for better efficiency, so I doubt
the yields of chloroform would be of any good unless the final pH is brought to about 9 or more (not that I would expect much of an yield of the final
intermediate anyway).
I would say, the perchlorination of citric acid might be of preparative use for the synthesis of trichloroacetate salts if someone ever develops a
preparative reaction, but as a route to chloroform it sounds as a waste of reagents in the view of the way more efficient (and economical) acetone
chlorination (even if made preparative). Related posts:
http://www.sciencemadness.org/talk/viewthread.php?tid=8378&a...
https://www.sciencemadness.org/whisper/viewthread.php?tid=14...
Edit: According to Naturwissenschaften, 1978, 65, 490 (DOI: 10.1007/BF00702843, attached), the non-catalyzed conversion of citric acid to chloroform is highest at pH 7. It decreases strongly at above
pH 8, and decreases at bellow pH 5.
Attachment: Larson&Rockwell_Citric acid-Potential precursor of chloroform in water chlorination.pdf (202kB)
This file has been downloaded 656 times
[Edited on 27/11/2013 by Nicodem]
…there is a human touch of the cultist “believer” in every theorist that he must struggle against as being
unworthy of the scientist. Some of the greatest men of science have publicly repudiated a theory which earlier they hotly defended. In this lies their
scientific temper, not in the scientific defense of the theory. - Weston La Barre (Ghost Dance, 1972)
Read the The ScienceMadness Guidelines!
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AJKOER
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Thanks Nicodem for your, as usual, informative comments.
A few points in response to your question "How can something old be new?"
First, the reference I cited, noting the role of Copper, was 2002 (and the article itself does refer to other recent work), and the study itself
refers to Copper salts and actually employs CuSO4. My method only employs the metal Copper itself. However, the Cu surface did have some dulling
(Copper oxide,..) and, at the end of my experiment, it appears to be returned to a new condition. The study explains the source of copper salts, in
the general water supply, as arising from corrosion (galvanic?) of copper pipes and the like. In short, no soluble Copper salt was employed and there
may have been some electrochemistry at work (in my opinion, not an exact replication of the 'old' work).
Second, while the NaCl only serves as an electrolyte in my intended reaction, I did cite an interesting reference noting the role of chlorides in
heightening the properties of HOCl (another relatively recent work). The role of chlorides was not examined in my cited source.
With respect to the 'non-preparative' comment, my reaction was considered non-preparative by me because I did not identify it as a possible path to
CHCl3 until I sought an explanation of what precisely occurred. As to whether it is a preparative approach of value, that is perhaps to be determined.
[Edited on 27-11-2013 by AJKOER]
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aga
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Not sure how i stumbled on this, but thought it worth a go yesterday.
 
No chloroform today. Not a sausage.
Maybe needs a reagent grade lemon 
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j_sum1
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Hmm. Lemon is not the same as citric acid despite the similar name.
Thanks for digging this up. If it actually works well tgen it deserves to become well known - especially as acetone becomes scarce in some parts. But
if it is impractical for some reason then that should be settled too.
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BromicAcid
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I think a better title would be "interesting chloroform preparation" or "unexpected chloroform preparation". Yes it was somewhat easy but it's no
easier than the old standby of mixing bleach and acetone. Still, thanks for sharing, for me it's definitely an unexpected reaction. I suppose the
copper cations are acting as ligands on the citric acid and activating one of the sites to substitution, and I would guess that it is one of the
methylene carbons that end up as the chloroform so two C-C bonds breaking.
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aga
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Well, lemons contain citric acid in significant quantity, plus it is all i have in the citric acid department.
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symboom
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The funny thing i was thinking of extracting limonene with chloroform so now i guess its all lemon based
Citric acid catalized by copper yields chloroform
Chloroform desolves lemonene from lemon peels
Fructose being in lemons
Fructose readily dehydrates to give hydroxymethylfurfural ("HMF").
with a lemon and bleach three solvents could be made
[Edited on 18-5-2018 by symboom]
[Edited on 18-5-2018 by symboom]
[Edited on 18-5-2018 by symboom]
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j_sum1
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Sounds like a competition. Maximum quantity of useful chemicals starting with lemons.
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JJay
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Not to rain on anyone's parade, but the haloform reaction works with ethanol, doesn't it?
I find very interesting this notion that it might be possible to make trichloroacetic acid and DCM from citric acid.
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AJKOER
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I would like to interject a point on perhaps an overlooked aspect of my bleach battery cell experiment from a new perspective of totally informed
hindsight.
Electrosynthesis can occur not only via standard electrolysis, but apparent also via an in situ formed electrochemical cell as well, per my
recollection (see as examples http://edepot.wur.nl/385426 and http://pubs.rsc.org/en/content/articlelanding/2010/gc/c0gc00... ).
In my experiment, I did in fact produced a battery cell, and given the added sea salt which may have promoted some solvated electron activity, one
could describe the process as an attempted electrosynthesis path to assist in the cleavage formation of chloroform from citric acid/citrate. Possible
reactions of interest would be:
HOCl -> HCl + 1/2 O2 (minor decomposition pathway)
O2 + e-(aq) = .O2- (see Table l, p. 14 at http://iopscience.iop.org/article/10.1088/0022-3727/48/42/42... )
Cl2 + .O2- = .Cl2- + O2 (see Reaction 36 at SUPPLEMENTAL SECTION PARTICIPATION OF THE HALIDES IN PHOTOCHEMICAL REACTIONS IN NATURAL WATERS AND
TREATED WATERS by Yi Yang and Joseph J. Pignatello)
HOCl + e-(aq) -> OH- + .Cl
.Cl + Cl- = .Cl2- (see https://books.google.com/books?id=mRoJUB5fxRwC&pg=PA321&... )
To test this hypothesis for those interested, if one repeats my experiment WITHOUT the presence of aluminum metal (which I usually source from
aluminum foil heated to red hot forming a more reactive gamma aluminum oxide coating rich in surface defects), one may observe lower or no yield of
CHCl3 (as there was no added cupric salt) if any electrosynthesis was likely involved.
-----------------------------------------------------------------
Another perhaps even more likely cause of the reduction of the citric acid is a fenton-type reaction between the Cu2O coating, forming a soluble
complex (L) with the citric acid (formed when I jump start the electrochemical cell in a microwave for 30 seconds in the presence of sea salt):
Cu(l)L + HOCl --> Cu(ll)L + .OH + Cl- (see "Fenton chemistry in biology and medicine" by Josef Prousek, reaction (15), p. 2330 at https://pdfs.semanticscholar.org/2b9b/92eff9ca32556c07b1a8cc... )
where the hydroxyl radical can attack the citric acid. There is also the possible creation of the chlorine radical:
.OH + Cl- = OH- + .Cl
And, depending on the chloride concentration, the less reactive, but longer life span, dichloride radical:
.Cl + Cl- = .Cl2-
Further, aiding in the recycling of the copper ions (in the presence also of complexing chloride) an equilibrium side reaction:
Cu(ll)L + Cu = 2 Cu(l)L
Interestingly, the presence of the aluminum electrode may keep the copper surface clean (that is a pure Cu electrode), the Al acting, in essence, as a
sacrificial electrode, to promote the above equilibrium reaction.
Also, to a limited extent also the presence of citrate (or ascorbate), as I noted previously on SM (see "Generation of Hydroxyl Radicals from
Dissolved Transition Metals in Surrogate Lung Fluid Solutions" by Edgar Vidrio, et al at http://www.ncbi.nlm.nih.gov/pmc/articles/PMC2626252/), can assist in the cycling of copper ions. To quote:
"Cu(II) + Asc(n) → Cu(I) + Asc(n+1) (R3)"
[Edited on 21-5-2018 by AJKOER]
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Boffis
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Interestingly I have observed a similar reaction while trying to oxidize malic acid to malonic acid with hypochlorite I too found that chloroform was
produced if the solution became too alkaline. Enough chloroform was produced in some reaction for it to separate and collect at the bottom. I failed
to make any malonic acid by this route and I wasn't really looking for chloroform and I have reported my experimental details already but in essence I
was mixing hydrochlorite with free malic acid to keep the reaction mixture acid/neutral but because there is a significant excess of NaOH in
commercial bleach the mixture eventually becomes alkaline and the smell of chloroform is immediately evident.
The curious feature of this reaction is that there is no methyl group in the molecule only a carbon with 2 hydrogens attached (a -CH2- group) which
must be the source of chloroform. Look at the structure of malic acid:
If chloroform was your target then it should be possible by neutralizing the acid with NaOH first.
Since citric acid contains 2 such CH2 groups adjacent to a hydroxyl bearing carbon I see no reason why it should not react similarly.
It would be interesting to know what the other products are. I originally thought that it would be oxalic acid but my investigations suggest that only
carbonate and anion forming soluble calcium salts are produced (glycolate or glyoxalate possibly).
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AJKOER
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I could explain the malic acid reaction with NaOCl/HOCl by the Fenton-type mechanism discussed above if there was some transition metal impurity
presence.
Otherwise, going to my provided "Fenton chemistry in biology and medicine" by Josef Prousek, a possible explanation by reaction (21):
ROO– + CO2 → [ROOCO2–] → RO• + CO3•– (21)
and another source (see https://www.ncbi.nlm.nih.gov/pmc/articles/PMC1219520/) citing radical formation on select organics from HOCl.
Any radicals created along with NaCl from the NaOCl/HOCl acting on the malic acid could induce further breakdown in the malic acid and with .Cl a path
to CHCl3.
[Edited on 21-5-2018 by AJKOER]
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clearly_not_atara
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Bromine water decarboxylates alpha-hydroxy acids by forming the corresponding hypobromite which undergoes a tandem decarboxylation /
dehydrohalogenation to give a carbonyl. See:
https://open.library.ubc.ca/cIRcle/collections/ubctheses/831...
Since citric acid and malic acid are also alpha-hydroxy acids, and HOCl is very similar to HOBr, it stands to reason the same thing occurs in these
cases. The acids are oxidatively decarboxylated to acetonedicarboxylic acid and formylacetic acid respectively. These are beta-carbonyl carboxylic
acid which decarboxylate to acetaldehyde and acetone respectively. Acetaldehyde and acetone are already known to yield chloroform upon reaction with
hypochlorite solution.
So nothing too mysterious is happening here, I don't think.
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aga
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Umm, perhaps i should clarify the outcome of the chlorocuprolemon experiment - i tried it and it didn't work.
Suppose i got to isolate citric acid from lemons now, via the Na-Ca-Citrate route to give it a proper go.
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Boffis
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@clearly_not_atara, that's interesting as it certainly described what I saw when I tried this reaction and also explains why I couldn't find any
organic anion amongst the insoluble calcium salts, the missing anion would be formate in my case.
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