| Pages:
1
2
3 |
LSD25
Hazard to Others
Posts: 239
Registered: 29-11-2007
Member Is Offline
Mood: Psychotic (Who said that? I know you're there...)
|
|
I remember reading somewhere that trifluoroiodomethane is formed by the reaction of trifluoroacetic acid with silver iodide. I know where
halodecarboxylation is concerned that there have been some serious moves away from silver salts to affect the reaction, so would other salts
halo-decarboxylate the trichloroacetic acid?
https://www.chem.ubc.ca/faculty/wassell/CHEM415MANUAL/Experi...
https://www.chem.ubc.ca/faculty/wassell/CHEM415MANUAL/Experi...
ie. heat the stuff in a vessel with iodine - is it possible to swap it?
Whhhoooppps, that sure didn't work
|
|
|
Nicodem
Super Moderator
Posts: 4230
Registered: 28-12-2004
Member Is Offline
Mood: No Mood
|
|
It is called the Hunsdiecker reaction and in the case of preparing CF3I surely requires I2 and silver trifluoroacetate (not trifluoroacetic acid and silver
iodide!). There was a bromobenzene thread where it was recently discussed. It requires the formation of RCOOX (where X is a halogen) type of intermediate which
decarboxylates to RX. Using it for preparing CCl4 would not be particularly practical unless one could use sodium instead of silver salt (and still
for small quantities only or proof of concept). Besides I don't even know how well, if at all, it works with X=Cl.
However, for CCl3X (where X=Br or I), this surely is a good route.
…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!
|
|
|
LSD25
Hazard to Others
Posts: 239
Registered: 29-11-2007
Member Is Offline
Mood: Psychotic (Who said that? I know you're there...)
|
|
I recently cited a number of articles on this very reaction where the author's used N-Halo reagents and other salts (lithium IIRC) to improve this
reaction. I think not_important was suggesting that the non-metal variant was not actually a Hunsdiecker-Borodin-the rest, reaction, but a separate
reaction altogether (that is if I understood correctly - which ain't always so). I recall that the various author's used predominantly halosuccinimide
reagents for this, but what are the chances that TCCA would work?
Whhhoooppps, that sure didn't work
|
|
|
Nicodem
Super Moderator
Posts: 4230
Registered: 28-12-2004
Member Is Offline
Mood: No Mood
|
|
Well, yes in theory (read: on paper) the reaction should work even on plain acid due to the equilibrium:
RCOOH + X<sub>2</sub> <=> RCOOX + HX
However halogens dissociate very badly in carboxylic acids and the above equilibrium is way to the left. Using a sodium salt of the carboxylic acid
would help moving the equilibrium more toward the right by lowering [HX] by neutralization (that is, by introduction of another equilibrium:
RCOO<sup>-</sup> + HX <=> RCOOH + X<sup>-</sup> . Yet
the [RCOOX] would still be too low for a rapid conversion to RX without side reactions prevailing (for example, when the decarboxylation takes too
much time most of the formed RX will succumb to the nucleophilic substitution with RCOO<sup>-</sup> forming the RCOOR ester). Using a
silver salt is optimal since it quantitatively and rapidly forms RCOOX due to the AgX precipitate forcing the equilibrium quantitatively to the right
(and still you often end up with low yields).
Surely one could try to use the free acid and exploit the above equilibrium even if far to the left by instead working on making the next step faster:
RCOOX <=> [RCOO* + X*] <=> [R* + CO<sub>2</sub> + X*] => RX + CO<sub>2</sub>
Yet that requires irradiation with UV light and I can only guess what other side reaction would such a treatment promote (one for example, is the
above thread talked about radical alpha-halogenation of carboxylic acids – the alternative to the HVZ reaction yielding the same products).
I checked if the Hunsdiecker reaction can be used in preparing alkyl chlorides and indeed it can be. However, mind that using silver carboxylates only
works with X<sub>2</sub>. Here you can not just substitute TCCA instead of Cl<sub>2</sub> since then you ruin the reaction by
not having the AgCl precipitation to drive the reaction. TCCA can only work in methods developed for N-chlorosuccinimide (NCS) if you can
find one such (and if there exist I bet they are substrate specific rather than general).
PS: Though this is still somewhat on thread topic it is only barely so and with the potential of straying away given it has little relevance for CCl4
or CHCl3 production, so I suggest you open a thread dedicated to the "Hunsdiecker-Borodin-the rest" reaction if you are really interested in it.
Surely several members would appreciate if you compile whatever information you have.
…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!
|
|
|
Sauron
International Hazard
Posts: 5351
Registered: 22-12-2006
Location: Barad-Dur, Mordor
Member Is Offline
Mood: metastable
|
|
Nicodem, the chloral review from CR did not mention side reactions, but stated that in the photolytic chlorination of chloral at temperatures above 10
C, no Cl3COCl was isolated, only CCl4 and the gaseous products from the radical fragmentation (CO, HCl, and sometimes small amount of COCl2.) This is
very clean.
The entire two step process starting with ethanol consumes only Cl2 (from TCCA and HCl) and in final stage only, UV. No other reagents. None.
So the sole advantage of stopping at first stage and utilizing the chloral react with AlCl3 and TCCA would be that a UV source would not be required.
The downside is that this is experintal. I hardly have anything against experimentalism (else I would not be here) but, it is not the path of least
resistance.
Side reactions and C2Cl6 formation were the problem with the perchlorination of acetyl chloride with 3 mols PCl5, an absurdly expensive approach I'm
sure even in the 19th century and insupportable today. 600g PCl5 to treat a mol of CH3COCl? That's seventy something grams substrate. And even so, the
C2H6 problem on reared its head at 200 C. By comparison the photolytic chlorination of chloral runs quantitatively at ambient temperatures.
I must admit I have not yet looked at those patents but as you say, TCCA was not among the examples andin general patents are not things I like to
base much of anything on. This is an old prejudice inculcated into me at university, that patents are about as reliable as Albanian politicians or
Iranian bazaaris.
I wish we could obtain the damned Boeseker paper from Rec.Trav.Chim. that I have been chasing for a year ever since seeing it in H.C.Brown's footnote
from 75 years gone. It details the use of AlCl3 to decompose chloral and/or trichloroacetyl chloride.
That decomposition of the acid chloride occurs under Brown's conditions with no UV and no AlCl3 to the extent of about 35-40%. Whether similar
thermolytic fragmentation will occur with trichloroacetic acid and TCCA, I do not know. We have found no examples of dichlorination or perchlorination
with TCCA, only monochlorination. The Trichlorination reactions on the acid chloride were only with PCl5 and do not seem to have ever seen any
replication in the 20th century.
My working hypothesis, till the rest of the refs are in, and we can start to get some experience with this, is that the ethanol-chloral-then UV to
CCl4 route is safe and sound.
Meanwhile the GAA or chloral to trichloroacetic acid route, is also sound, but the path from that point to CCl4 via AlCl3 is ill lit and requires some
slashing at vines and hacking of trails, i.e., wet lab time.
So one is a solid preparative route and the other a good start to a research project. My concern is shortest distance from here to CCl4 with the least
resistance. You, as you mentioned, are blessed with circumstances where CCl4 is off the shelf. Lucky you! Unfortunately I do not share this happy
state. So while I share youe enthusiasm for thus new adventure, I prefer the surer path for the present.
Sic gorgeamus a los subjectatus nunc.
|
|
|
Sauron
International Hazard
Posts: 5351
Registered: 22-12-2006
Location: Barad-Dur, Mordor
Member Is Offline
Mood: metastable
|
|
I read that US patent. Here it is in case anyone else wants to have a look.
Not very interesting.
Nicodem, the trichloroethane (I guess 1,1,1-trichloroethane) ubiquitous solvent you were talking about, There was a discussion of an old patent last
year in regard to making Ac2O or acetyl chloride from this. But the patent was very broad and vague, and examples they gave required an autoclave.
Chloroacetyl chloride was not a product.
That's the only discussion I recall involving 1,1,1-trichloroethane.
[Edited on 8-4-2008 by Sauron]
Attachment: US2613220.pdf (384kB)
This file has been downloaded 680 times
Sic gorgeamus a los subjectatus nunc.
|
|
|
trilobite
Hazard to Others
Posts: 152
Registered: 25-2-2004
Location: The Palaeozoic Ocean
Member Is Offline
Mood: lonely
|
|
I don't think that a radical pathway is needed to explain the decomposition of the halogenated acyl halides. I assume that the reaction proceeds
through formation of a di- or trichloromethyl carbocation stabilized by the electronegative chlorine atoms. Obviously both Brönsted and Lewis acids
catalyze the reaction.
These are not the only acyl halides where such phenomena can be observed. For example when pivaloyl chloride (aka trimethylacetyl chloride) is used in
a Friedel-Crafts acylation of benzene most of the acyl chloride is decomposed with liberation of carbon monoxide and the resulting tert-butyl
carbocation alkylates the substrate. If I remember correctly the experimental result was that if the temperature is kept low enough some pivaloylated
product can be isolated, but most of the product consists of tert-butylbenzene.
I dug up some abstracts and references relating to the subject. Some of them discuss the reverse reaction, formation of the acyl halides through
carbonylation, while others discuss the Friedel-Crafts reactions without decarbonylation.
Catalytic Action. III. 1. Friedel-Crafts Reaction.
Boeseken, J.
Delft. Rec. trav. chim., 29, 85-112 (1910)
Abstract
The author believes that catalysts do not react through intermediate addition products but by changing the affinities for each other of the ats. in
the reacting substances, an at. or group of ats. being either (1) entirely eliminated from the rest of the mol. and reacting as such or (2) activated
without being separated from the rest of the mol. E. g., (1) when SOCl2 reacts with PhCl and AlCl3, no dichlorodiphenylsulphone, but only
polychlorobenzene, is formed; (2) BzCl and C6H6, in the presence of AlCl3, give BzPh. This dissociating action of AlCl3 was investigated with chloral
and substituted Ac chlorides. Trimethylacetyl Chloride is decomp. very energetically by AlCl3 even at 0 Deg into HCl, CO and isobutene, C4H8. At
ordinary temp. H2SO4, which in many respects is analogous to AlCl3 as a catalyst, liberates HCl from Me3CCOCl with formation of Me3CO.SO4H. On
warming, CO is set free and the isobutene dissolves in the H2SO4 to form isobutenedisulphonic acid, C4H6(SO3H)2. Chloral is decomposed chiefly into
CO, HCl and CCl2 which polymerizes to C2Cl4. If less than 1 mol. AlCl3 is used and the duration of the reaction prolonged, other products, such as
COCl2, C2Cl6, C5H2O3Cl6 (chloralide), are formed in small quantity. Dichloroacetyl Chloride with excess of AlCl3 gives CHCl3 and CO. With smaller
quantities of AlCl3, much HCl and little CO is evolved at first, then the amount of CO increases and a compd. C5H10, which is probably
perchloropentamethylene, needles, m. 32 Deg, b45 132 Deg, is obtained. Trichloroacetyl chloride is very slowly decomposed by AlCl3 into CO and CCl4.
Reactions of carbon monoxide and sulfur dioxide with polychlorinated methanes.
Frank, C. E.; Hallowell, A. T.; Theobald, C. W.; Vaala, G. T.
Journal of Industrial and Engineering Chemistry (Washington, D. C.), 41, 2061-2 (1949)
Abstract
Chloroacetyl chlorides are obtained from CO and polychlorinated methanes at pressures of 850-950 atm. and in the presence of an AlCl3 catalyst.
Optimum conditions for the prepn. of Cl3CCOCl comprise the use of 0.1 mole AlCl3/mole CCl4 at 200 Deg and 950 atm. CO pressure for 2 hrs. Beyond a
certain min., time is not crit. Reaction begins at 100 Deg and a CO pressure of 50 atm. Polyhalogenated ethanes also react with CO, but the yields
of acyl halides are low due to side reactions. SO2 can be made to react with CCl4 or CHCl3 to give SOCl2. With an excess of SO2 and in the presence
of AlCl3, yields of 70-80% were obtained. The AlCl3 retains some activity after use.
Patents related to the invention are US2378048 and GB581278.
Reaction between aromatic compounds and derivatives of tertiary acids. V. The stability of the carbonyl group in certain acid halides and
anhydrides
Rothstein, Eugene; Saville, Rowland W.
Journal of the Chemical Society, 1949, 1961-8
Abstract
The factors influencing the acylation or alkylation of aromatic compds. by derivs. of acids in the Friedel-Crafts synthesis are discussed. It is
suggested that the stability of the acyl cation [R3CC+O] dets. the relative rates of the 2 processes. Loss of CO results in the formation of an
electrophilic carbonium ion [R3C+], which can be substituted in the nucleus, yield an olefin, or undergo rearrangement. The effect of substituents on
the relative ease of elimination of CO is also examd. and it is shown that the decompn. may be used for the detn. of the course of the reaction.
Thus, condensation of diarylacetyl chlorides with C6H6 is attended by the simultaneous liberation of CO; this was not detected by previous workers in
this field and, in consequence, an explanation advanced by McKenzie, et al. (C.A. 27, 81), of the formation of Ph2CH2 and Ph3CH from p-MeC6H4CH-PhCOCl
is untenable. These diarylacetic acid derivs. provide the 1st instance of an unstable secondary acyl ion, Ar2CHC+O. Me2C(COCl)2 (13.5 g.), 22 g.
AlCl3, and 140 cc. C6H6 give 52% Me2CBz2 and a negligible vol. of CO; 14 g. Me2C (COCl)2, 23 g. AlCl3, and 6.5 g. C6H6 in 120 cc. CS2 give 8.1% CO,
23% iso-PrPhCO, 8.1% Me2CBz2, and 0.5 g. 2,2-dimethyl-1,3-indandione(?); similar results were obtained with Et2C(COCl)2. ClCH2COCl and C6H6 give 87%
BzCH2Cl and 17% CO; Cl2CHCOCl gives 79% BzCHCl2 and 3.6% CO; Cl3CCOCl gives 56% BzCCl3; Cl3CCOBr gives the same result. Me2CBrCOCl and Me2CBrCOBr
give 2-methyl-1-indanone and Me2CBrBz. Camphoric anhydride (I) (10 g.) in 160 cc. C6H6, treated with 15 g. AlCl3, gives 89% CO and 67%
2-phenyl-1,1,2-trimethyl-5-cyclopentanecarboxylic acid and a small quantity of a hydrocarbon m. 80-1 Deg; PhOMe gives 3.4% CO and 89% 5(or
2)-anisoyl-1,1,2-trimethyl-2(or 5)-cyclopentanecarboxylic acid. PhMe yields 3% CO and 82% of the 2-toluyl deriv. PhCMe3 (10.5 g.) in 10 cc. CS2,
added to 7 g. I, 10.5 g. AlCl3, and 70 cc. CS2 at 0 Deg and warmed, give 74.2% CO, 2.7 g. PhCMe3, a smaller quantity of p-C6H4(CMe3)2 and, after
methylation, Me 2-(p-tert-butylphenyl)-1,1,2-trimethyl-5-cyclopentanecarboxylate, b0.2 110-15 Deg. PhNHAc yields mainly Me isolauronolate.
p-MeC6H4CHPhCOCl and C6H6 with AlCl3 in CS2 give 70% CO and 33% Ph3COH; PhOMe yields little CO and 88.6% methoxyphenyl a-p-tolylbenzyl ketone, m.
107-8 Deg. Ph2CHCOCl and C6H6 give 68% CO and BzCHPh2. Et2CHCOCl and C6H6 yield 7% CO and 81% BzCHEt2 (2,4-dinitrophenylhydrazone, m. 115-16 Deg).
AcNHCH2-COCl and C6H6 give 8% CO and BzCH2NHAc.
Decarbonylation of chloroacetic acid chlorides in the presence of aluminum chloride
Pomerantseva, E. G.; Kulikova, A. E.; Zil'berman, E. N.
Zhurnal Organicheskoi Khimii, 5(1), 187 (1969)
Abstract
Heating a mixt. of ClCH2COCl and AlCl3 gave CO, HCCCl, and a polymer (I) with conjugated double bonds. Similarly, Cl3CCOCl with AlCl3, gave CO, CCl4,
ClCCCl, and a polymer. Heating CH2Cl2 with AlCl3 also gave I. A mechanism is proposed.
Direct carbonylation of polychloroalkanes to acid chlorides using metallic salt ternary systems: An example of multistep catalysis.
Monflier, Eric; Mortreux, Andre; Petit, Francis; Lecolier, Serge.
Journal of the Chemical Society, Chemical Communications, 1992(5), 439-41
Abstract
A catalytic cycle for the direct carbonylation of CCl4 to CCl3COCl, catalyzed by metal salt mixts., e.g., AlCl3/MCln/CuCl, under unexpectedly mild
conditions, is proposed on the basis of FTIR, 17O and 27Al NMR spectroscopic studies.
Patents related to succesful Friedel-Crafts trichloroacetylation of substrates are EP189266, US4724267, US4731484, FR2677645. DE2648134 is about
synthesis of trichloroacetyl chloride from CO and CCl4.
|
|
|
Sauron
International Hazard
Posts: 5351
Registered: 22-12-2006
Location: Barad-Dur, Mordor
Member Is Offline
Mood: metastable
|
|
Thanks. That argues against the use of AlCl3.
Those reactions do not proceed cleanly. Numerous side products form.
In comparison, the photolytic chlorination of trichloroacetaldehyde in absence of AlCl3, certainly a radical reaction, proceeds exclusively to CCl4
(and CO and HCl) and there is no reverse reaction.
This reaction takes place at temperatures from beloe ambient (such as 10 C) to 90 C.
Only at -10 C and below does any intermediate Cl3CCOCl survive. At 10 C, 7.5% and at -50 C, 55%.
Sic gorgeamus a los subjectatus nunc.
|
|
|
Sauron
International Hazard
Posts: 5351
Registered: 22-12-2006
Location: Barad-Dur, Mordor
Member Is Offline
Mood: metastable
|
|
The preparation of chloral by reaction of 1,1,1-trichloroethane with aqueous hypochlorous acid is subject of a US patent. This may have been what
Nicodem had in mind rather than that catalytic reaction.
Meanwhile I reread two patents from my files on chlorination of ethanol. These teach that 95% ethanol can be used instead of anhydrous, and unlike the
chloral review, make no mention of cooling to 0 C in the initial (oxidation) stage of the reaction.
Chlorination of ethanol is in any case a much faster process than chlorination of glacial acetic acid to same degree of chlorine content and requires
no UV irradiation.
Ethanol perchlorinates to chloral in about 6 hours compared to 60 hours for GAA to trichloroacetic acid.
Normally 2 mols ethanol are chlorinated to one mol chloral "alcoholate" (trichloroacetaldehyde ethyl hemiacetal) and chloral is then liberated with
conc H2SO4 by distillation.
----------------------
Back on MeSCN
The hangup in the DMS route to MeSCN is barium thiocyanate, which is very costly; and it can be made from ammonium thiocyanate, also relatively dear.
Ammonium thiocyanate is made from ammonium dithiocarbonate, and that is made by adding NH3 to CS2 in water. Inorg.Syn. has the prep, I will have to
look more closely to see if this is economically competitive with the alternative, which is to use DMS to make MeI, then react MeI with KSCN in EtOH.
CS2 is after all rather costly.
[Edited on 9-4-2008 by Sauron]
Attachment: 2616929[1].pdf (138kB)
This file has been downloaded 598 times
Sic gorgeamus a los subjectatus nunc.
|
|
|
Sauron
International Hazard
Posts: 5351
Registered: 22-12-2006
Location: Barad-Dur, Mordor
Member Is Offline
Mood: metastable
|
|
Preparation of Chloral (Trichloroacetaldehyde) per Rosin's Patent
An apparatus is assembled consisting of a 1 liter RB flask with four necks, a termometer or thermocouple adjusted to nearly the bottom of the flask, a
mechanical stirrer and an efficient reflux condenser and a gas inlet tube with coarse fritted tip. The flask is supported in a heating mantle. The
condenser is topped with a gas outlet tube leading to a large caustic trap for receiving HCl produced in the reaction and any Cl2 not absorbed.
The gas inlet tube is connected to a chlorine gas generator charged with TCCA and equipped with a dropping funnel or other means of admitting 5 M
hydrochloric acid at a controlled rate. The 5 M HCl is prepared by cuatiously mixing equal volumes of concentrated hydrochloric acid and water.
The chlorination flask is charged with 200 cc (3.37 mol) 95.5% ethanol, the stirrer is started, and chlorine is admitted at a rate of approx. 3.5 g
per minute for about 2.5 hours. The temperature of the reaction mixture will have risen substantially during this stage of the chlorination, and
condenser water is recirculated through a chiller to reflux any vapors. The reaction mixture at this point will weigh about 260-280 g and have a
density of c. 1.29-1.35 @ 25 C. The material is now principally dichloroacetaldehyde ethyl hemiacetal. The caustic trap will have increased in weight
by about 245 g.
120 ml water is now added to the reaction mixture.
The chlorine rate is now reduced somewhat to 2.5 g/min, and the reaction mixture is maintained at reflux by use of the heating mantle until the
boiling point reaches 95 C. This process takes about a further 8 hours. The chlorination is complete for practical purposes when the weight of the
reaction mixtures has reached 500-550 g and it has a density of 1.50-1.57 @ 25 C. Heating and chlorine generation are not halted. The reaction mixture
is allowed to cool to room temperature and is then mixed with an approximately equal volume of concentrated H2SO4, thus liberating chloral from its
hydrate. Upon distillation 364 g chloral is obtained. (73% yield).
Sauron's notes:
3.5 g/min x 150 min = 525 g Cl2 generated in initial phase.
2.5 g/min x 480 min = 1200 g Cl2 generated in second phase.
Total chlorine generated 1725 g
So we can calculate the amount of TCCA required, the amount of 50% dil HCl needed and the parameters of the caustic scrubber. I estimate it will
require c. 5 Kg TCCA to generate 1725 g Cl2. That is based on 4 mols TCCA to the Kg (actually that figure is a little low) and about 90 g available
Cl2 per mol TCCA (which is about right.) A Kg TCCA requires about 2.4 L of 5 N HCl, so about 12 liters (made from 6 liters conc HCl and 6 liters
water) will do the trick.
It seems like > 30% of the generated chlorine is going to waste most likely in the latter stage of the chlorination, and ends up in the scrubber as
chlorate and chloride.
Overall stoichiometry under anhydrous conditions
2 CH3CH2OH + 4 Cl2 -> Cl3CCH(OH)(OCH2CH3) + 5 HCl
Overall stoichiometry when water is added
CH3CH2OH + 4 Cl2 + H2O -> Cl3CCH(OH)2 + 5 HCl
Both of these and the production of chloral diethyl acetal are all happening here. The point of Rosin's patent is to maximize the chloral hydrate vs
the chloral alcoholate so as to make better use of the ethanol. He claimed about 60% more chloral from a given amount of ethanol by this method.
One final comment regarding chlorine absorption and generation:
My estimates are based on Rosin's stated rates for the first 2.5 hours (3.5 g/min) and the following 8 hours) 2.5 g/min). The assumption, very likely
faulty is that these are constant. I think in practice it is better to shoot for about 3 g/min throughout, this may lengthen the first stage a little
and reduce time of second stage a little, those points are determined by weight and density not by the clock. Also the real limiting factor is the
capacity of the reflux condenser.
It is highly likely that the chlorine generation will slow down over time and require gentle heating to drive it. Or the chlorine generator may need
recharding with TCCA and HCl. Trial and error will determine the appropriate scale to achieve target 3 g/min flow rate and how to keep that rate for
10-11-12 hours. The correct flow rate is determined by chlorine absorption in the reaction, so the off gases need monitoring. The appearance of
yellow green Cl2 means, slow down the Cl2 flow. This would be easily done from a tank, but from a Cl2 generator, that's another story. Trial and
error will determine the best conditions.
The chloral once isolated from conc H2SO4 is ready to be either converted to CHCl3 with base, which is a reaction dependent on both pH and
temperature; or charged to a photochemical reactor for irradiation and chlorination to trichloroacetyl chloride, which falls apart to CCl4, CO and
HCl. I propose to do this in a 5 liter Ace setup using a 450 W Hanovia high pressure Hg-quartz arc lamp #7825-35 in a quartz immersion well, the
amount of charge being sufficient to cover the full length of the arc. Ace has both conical and spherical reactors in this size. I have located a
second hand power supply to match, a 7830-60 and this will save me some money.
Given the equipment at hand, the largest scale I can run is about 1 Kg chloral product per day so I will probably only do the photochemical step once
every 3-4 days (and in the hood.) I have to build a containment for it to avoid UV exposure. The CCl4 product should about equal the chloral charge
according to the mass balance. So maybe a week's work to produce 6-7 L CCl4. And that drum of TCCA will need replacing.
[Edited on 10-4-2008 by Sauron]
Sic gorgeamus a los subjectatus nunc.
|
|
|
Sauron
International Hazard
Posts: 5351
Registered: 22-12-2006
Location: Barad-Dur, Mordor
Member Is Offline
Mood: metastable
|
|
Again on MeSCN:
The preparation of ammonium dithiocarbonate is described starting on page 48 of Inorganic Syntheses vol 3.
NH3 is bubbled into a solution of CS2 in isopropyl acetate at 25-30 C.
Yields are 92-96%.
According to Ullmann's the unstable dithiocarbonate is decomposed at 95 C to ammonium thiocyanate, H2S and S.
The preparation of barium thiocyanate from ammonium thiocyanate and barium hydroxide is described in same volume of IS starting on page 24.
This salt is reacted with dimethyl sulfate to give methyl thiocyanate.
In my opinion, it is better to utilize the DMS to prepare MeI from KI according to Org.Syn., then react the MeI with KSCN in EtOH according to Vogel.
The virtue of the second route is that no CS2 is required and fewer steps are involved. Both routes use DMS. I will have to look at the economics of
this vs buying MeI or buying MeSCN, because if buying MeI is not so costly, then avoiding use of DMS is a good thing. I have the stuff, but. But.
Sic gorgeamus a los subjectatus nunc.
|
|
|
woelen
Super Administrator
Posts: 7976
Registered: 20-8-2005
Location: Netherlands
Member Is Offline
Mood: interested
|
|
According to my calculations, you will need almost 4 kg of TCCA (theoretically). In practice, probably you are right with your estimate of 5 kg,
because at the end the reaction will become very slow, due to all the cyanuric acid, which makes mixing of dripped acid with the remaining TCCA more
and more difficult.
If I were you (and if you have the right tubing), I would make a setup with 2 chlorine generators, connected to a T-shaped glass tube. First, you use
one chlorine generator, and if this becomes too slow, you use the other and stopper the end on the T-tube for the exhausted one. In this way you can
recharge the first one, while the second one is running. In this way, you could use alternating chlorine production with small generators. I think
that nice steady flow of chlorine gas for so many hours will be very difficult to achieve, hence my suggestion of using alternate generators with
smaller quantities of TCCA.
My experience with TCCA is quite good, when it comes to purity of the chlorine, but a constant rate is difficult. You'll observe a gradually
decreasing rate, as more and more cyanuric acid builds up. With respect of constant production rate, tablets (not powder or granules!!) of Ca(OCl)2 is
better.
|
|
|
Sauron
International Hazard
Posts: 5351
Registered: 22-12-2006
Location: Barad-Dur, Mordor
Member Is Offline
Mood: metastable
|
|
Thanks, the alternating Cl2 generator suggestion is very good. I appreciate the input.
Sic gorgeamus a los subjectatus nunc.
|
|
|
| Pages:
1
2
3 |
|
![[*]](images/xpblue/default_icon.gif){kind=icon}
