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Solvent extraction of nickel

Dear Reader,

I was thinking about solvent extraction recently, now solvent extraction a bit more than “shake A and B, and the nickel extracts”. Rather than merely shaking things and seeing that the metal goes from one layer to the other (and stopping there) it is important to understand that a lot of things can control the equilibrium position. I was recently thinking about nickel with BTBP.

I made the assumption in this model of the thermodynamics that the nickel reacts with the BTBP in the bulk of the aqueous phase and that no reaction occurs in the organic phase. I make a lot of use of Hess’s law.

Some years ago I was involved in a study of the solvent extraction chemistry of nickel with the BTBP reagents. Here are some equations which I have written which help explain things.

Extraction behavior of nickel(II) using some of the BTBP-class ligands, Ekberg, C., Dubois, I. Fermvik, A., Retegan, T., Skarnemark, G., Drew, M. G. B.,Foreman, M. R. S. and Hudson, M. J. SOLVENT EXTRACTION AND ION EXCHANGE, Volume: 25, Issue: 5, Pages: 603-617, DOI: 10.1080/07366290701512634, Published: SEP-OCT 2007

At low concentrations of C6-BTBP the following equation is true.

Log D = Log K + log [BTBP]

Where D is the distribution ratio, K is an extraction constant and [BTBP] is the concentration of the BTBP in the organic phase. But when the concentration of the BTBP is higher then this equation

Log D = Log K’ + 2.5 log [BTBP]

When it is even higher the best equation becomes

Log D = Log K”

This paper clearly in figure 4 shows that the nickel distribution ratio reaches a plateau when the BTBP concentration reaches a value of about 1 mmol for C6 BTBP.

What I want you to do is to consider a BTBP which distributes between the organic and the aqueous phase.

Kd(BTBP) = [BTBP]org/[BTBP]aq

Then if the BTBP is able to bind to the nickel we can write the following two equations

k1 = [NiBTBP]aq/[Ni]aq[BTBP]aq

β2 = [Ni(BTBP)2]aq/[Ni]aq[BTBP]2aq

And then we combined these equations we get

[Ni]aq / total aqueous nickel = 1 / (1 + k1[BTBP]aq + β2[BTBP]2aq)

[NiBTBP]aq / total aqueous nickel = k1[BTBP]aq / (1 + k1[BTBP]aq + β2[BTBP]2aq)

[Ni(BTBP)2]aq / total aqueous nickel = β2[BTBP]2aq / (1 + k1[BTBP]aq + β2[BTBP]2aq)

Now we are about to add the physical distribution of the three forms of nickel between the aqueous and organic layers, we will use equations like this

Kd(Ni) = [Ni]org/[Ni]aq

Kd(NiBTBP) = [NiBTBP]org/[NiBTBP]aq

Kd(Ni(BTBP)2) = [Ni(BTBP)2]org/[Ni(BTBP)2]aq

I want you to combine these equations to get to now give us (take a deep breath), and trust me this will be pleasureable !

DNi = (Kd(Ni) / (1 + k1[BTBP]aq + β2[BTBP]2aq) + (k1[BTBP]aq/Kd(NiBTBP) / (1 + k1[BTBP]aq + β2[BTBP]2aq)) + ( β2[BTBP]2aqKd(Ni(BTBP)2)/ (1 + k1[BTBP]aq + β2[BTBP]2aq))

Now we take another step to include the constant Kd(BTBP) we get an even bigger equation which is harder to write here on wordpress. But I imagine that you will have no problem with it.

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Poisoned milk (snake attack)

Dear Reader,

I have noticed a rather odd and deeply sad case which has been reported from India (Uttar Pradesh state). It has been reported that a 35 year old woman was bitten in her sleep by a poisonous snake, after she woke up she breast fed her three year old daughter. Sadly both of them passed away before they could reach medical help.

I looked up the nature of the venom of a cobra and it is a protein (polypeptide) with several loops of amino acids. The protein crystallographic data base (PDB) has an entry for the King Cobra venom.

Some time ago while at Scandevium in Göteborg, I was talking to a snake expert. I asked a question which I had always woundered about “is a snake immune to its own venom ?”. The snake worker said “no, if a snake was to bite itself then it could poison itself”. The interesting thing is that if the snake injects other animals with its poison. The snake then eats the dead animals, so surely the snake needs to be immune to its own poison when it swallows it.

The problem is that swallowing is a different exposure route to an injection. I worry that something odd has happened in India. I would expect the woman to suffer from the ill effects of the snake bite. But as the venom is a protein I would expect that the digestive system of the child would degrade it and thus render it far less toxic. Also the human digestive system does not normally allow proteins to pass from the gut contents into the blookd. When a person’s digestive system does start to allow a protein to cross in this way is the basis of an allergy to a particular food such as chicken.

I will make some searches of the academic literature and I will attempt to contact some snake experts to ask them about this sad case.

SWR paint

The spoof SWAR-grease advert in the 2017 april edition of RadCom made me smile. Many years ago as a teenager there was a joke doing the rounds about a special paint which would improve the SWR of your aerial. The idea was that your painted your aerial with this magic substance. All very funny, but there is more to it than you might think. If an aerial were to be coated with a thick layer of something with a higher relative dielectric constant than air then the resonant frequency of the aerial will decrease. If we start by thinking of a monopole aerial with a ground plane.

monopole aerial

Then this will have a resonant frequency, but when we add the dielectric cladding (in magenta), then the resonant frequency of the monopole will decrease.

monopole aerial with dielectric cladding

Thus if a very thick layer of “SWR paint” was applied to any aerial then the aerial would be useable at lower frequencies. Some years ago in the 1970s some papers on the subject were written by J.R. James et. al., here they expressed themselves with Smith charts which are nice and easy to understand. Chung-Yu Ting in the 1960s wrote some excellent papers on the topic in which he expressed himself with what I would describe as “extreme algebra”. While some people might not like Smith charts, I suspect that like myself many people would prefer a Smith chart to a wall of algebra.

Also if the coating of the aerial was a substance which is a lossy dielectric then this would increase the resistive losses in the aerial. I would expect that the aerial would be more easy to match with an ATU as it would be more lossy. Also the aerial would appear to be more wideband as the losses would make the changes in impedance as the frequency changes to be less obvious. I know that a 50 ohm resistor makes a very “good” wideband aerial in terms of SWR bandwidth, just sadly the gain of this “aerial” is rather bad.

Cyanide theft

Dear Reader,

It has come to my attention that a man (Richard O’Rourke) in the USA has been arrested and dismissed from his job for the alleged act of stealing a large amount of potassium cyanide. He also accused of having dumped the cyanide into the drainage system which is clearly not a good idea. It is reported that he stated that he took the cyanide to kill rats which were on his property.

To my mind potassium cyanide does not seem like the ideal tool for expunging rats from your property. I cannot imagine rats being so obliging that they will eat from a simple pile of KCN. I expect that one would have to formulate the KCN into a poisoned bait. I have heard a story that the reason the attempt on Rasputin using cyanide failed was that the cyanide was baked into a sugar rich cake. I imagine that a combination of a sugar such as fructose would react with the cyanide in the Kiliani reaction to form something much less toxic. In the same way I would expect that on mixing with corn syrup, treacle or some other sweet food which would be attractive to rats would cause the Kiliani reaction to occur.

The chemistry world article wrote of how the people at King’s College London use hydrogen peroxide to destroy unwanted cyanide in the lab. I have checked and hydrogen peroxide will react with cyanide. It is claimed that it has some advantaged over the use of chlorine based oxidants. Some academic papers have been written on the subject of cyanide destruction using hydrogen peroxide.

I have never tried hydrogen peroxide for disposing of cyanide, I have always used chlorine bleach or the conversion of cyanide into Prussian blue. During my time on the PARTNEW and EUROPART projects I used to run reactions with far more cyanide than Eileen Cheng describes. Reactions with about 80 grams of KCN in each pot soon became routine As long as you are careful it can be done safely, also always run reactions on a small scale before scaling up.

The late Donald Myers (G8AYG) was a pharmacist I knew from the Loughborough amateur radio club, he told me once a clergyman went to see him with a jam jar containing a white solid. The clergyman had remarked one Sunday to a member of his flock that he was troubled by a wasps nest. The next Sunday a farmer walked up to him and presented him with the jam jar with the suggestion of “tip it into the nest”. The clergyman did not know what the solid was and was a bit worried, Don agreed to examine it and deal with it. When Don opened the jar he quickly became aware that it was either NaCN or KCN. Don reacted the cyanide with ferrous sulfate, he then said that he put the jar on the roof of the pharmacy with some cover to keep out the rain. He said that he imagined that the jar might still be there and how he expected that the residues will have aged and weathered by now. I suspect that the mixture might have turned into Prussian blue by now

A word of useful advice, never assume that cyanide is safe to discharge into the drains if it is coordinated to iron as [Fe(CN)6]4- or [Fe(CN)6]3- . On exposure to light these complexes can release cyanide anions and are thus a threat to fish and other lifeforms. I have always found that you can however convert cyanide waste to [Fe(CN)6]4-, add an excess of iron sulfate, boil it and finally add some acid to form a slurry of Prussian blue. I used to then dispose of the solid. Prussian blue has the interesting ability to remove cesium from farmyard animals (and humans) by acting as a cation exchanger. The normal dose for adult humans is 3 grams a day but in extreme cases the dose can be increased to 30 grams per day. The problem is that Prussian blue is very variable in composition and particle size. Josef Novosad worked on the use of Prussian blue to decontaminate cesium from farmyard animals he told me that each batch of Prussian blue he made was unique.

I have written elsewhere about Prussian Blue, about the chemical bonding in it. I have also written about how Prussian blue retains potassium (or cesium) ions.

Poisoned car door

Dear Reader,

Reports are coming in suggesting that poison smeared on a car door might be responsible for the serious injuries suffered by the Skripals. It is interesting that the labour leader is calling for a more open discussion of the evidence associated with the poisoning.

I also find it interesting that the inventor of the Novichok agents is making a statement on the likely long term effects of the substance on the general public. Looking at his statement I see a problem which can exist, all of the nerve agents work by altering a key enzyme in the nervous system.

I reason that the reason why these substances can cause serious injury is that they greatly reduce the amount of the active enzyme in the body at one moment. One could regard this effect as being due to the nerve agents simply lowering the concentration of this enzyme.

While there are some differences in the rates of both reactivation and further inhibition by the different nerve agents in terms of their mechanism the classic nerve agents are all the same in terms of how they cause the acute effect. What happens is that the nerve agents normally bind to an OH group in the enzyme (on a serine residue). For many of the chemical warefare agents they tend to then lose an alkoxy group thus making it harder for the enzyme to become reactivated as shown below.

sarin binding to enzyme

However it is known that a delayed condition known as organophosphate-induced delayed polyneuropathy exists. According to Milan Jokanović and Melita Kosanović the OPIDP normally appears within 10 to 20 days of a one off exposure. So I suspect that unless the Novichok agents have some special ability to bind to some important biomolecules which are very rare in a human when compared with acetylcholinesterase and the other things which the “normal organophosphates” bind to that if the general public manage to stay healthy for a month after the event then they should remain healthy. That is assuming that something else does not go wrong with them.

It is interesting that a lot of phosphorus compounds are used as enzyme inhibitors, for example the herbicide “roundup” is N-(phosphonomethyl)glycine which is the chemical of choice for many people who want to keep their drive free of weeds.

References

Milan Jokanović and Melita Kosanović, Environmental Toxicology and Pharmacology, 2010, 29, 195-201.

The Novichok agents

Dear Reader,

Things have become more complex in more ways than one, it has been claimed in the UK that the nerve agent attack involved a so-called novichok agent. I also posted this post to the wrong blog last night.

Now I can not claim to know where these novichok agents came from, who did it or even if a novichok agent was used. I would rather not get sucked into a debate about who did it, I am mainly going to consider the chemistry.

However I can consider some of the chemistry, according to the internet the novichok agents were invented in the Soviet Union in an attempt to make chemical warfare agents even worse than sarin and VX. On Wikipedia it is claimed that methyl-(1-(diethylamino)ethylidene)phosphoramidofluoridate and 1-chloropropan-2-yl (E)-(((chlorofluoromethylene)amino)oxy)phosphonofluoridate are examples of novichok agents.

1-chloropropan-2-yl (E)-(((chlorofluoromethylene)amino)oxy)phosphonofluoridate

Part of the problem is that very little if anything has been written in the academic literature about novichok agents, well at least under that name. I did a search of the web of science and I did not find any mention of any paper with that word in the topic or title on the subject of chemical warfare. On the other hand I found almost 800 papers which have the word “sarin” in the title.

I also looked for methyl (E)-(1-(diethylamino)ethylidene)phosphoramidofluoridate in the organic chemistry literature using one common database, and I could not find any mention of this substance. Looking at it as a organophosphorus chemist I can see that it has the correct groups attached to a phosphorus atom to act as an acetylcholinesterase inhibitor. I also see an electron releasing group which would reduce the partial positive charge on the phosphorus atom when it is compared with sarin. This reduction in partial positive charge would reduce the rate at which the substance will react with water. This change would be likely to make the substance more able to persist in the environment.

However when you look for 1-chloropropan-2-yl (E)-(((chlorofluoromethylene)amino)oxy)phosphonofluoridate you can find plenty written on the subject in the Soviet chemical literature back in the 1960s and 1970s. By reacting dichlorofluoro(nitroso)methane with a phosphorus(III) compound a reaction similar to the Arbuzov reaction occurs which forms the product. Here is my best effort for the mechanism by which the compound is formed.

reactionoftrihalonitromethane

I hold the view that while the Soviets are thought to have developed the novichok compounds it would not be very hard for a competent (and well protected) phosphorus chemist to make a moderate amount of one of these rather exotic substances. So unlike polonium-210 (which is only produced) in very few nuclear reactors it is impossible to argue based on the identity of the nerve agent where it came from.

One of the problems in life is that sometimes bad people will choose tools or methods which are not normally used by people from their country in an attempt to confuse any investigator. For example the NKVD used German pistols to murder Polish officers at Katyn. This offers some degree of plausible deniability. Thus I think some other evidence other than the identity of the nerve agent is required before anyone can blame anyone for the horrible event which has just occured.

Mrs May and the nerve agent

Dear Reader,

It has come to my attention that Mrs May the prime minister of the UK has made a public statement in which she suggested that it was likely that Russia was in some way responsible for the poisoning of people in the UK.

The problem is that based on the information which has been released into the public domain it is not possible to prove that a “military grade” nerve agent was used. Even with the benefit of a PhD and some further experience of organophosphorus chemistry I have to confess that I do not know what a “military grade nerve agent” is.

I note that the cult in Japan which used sarin was not part of the military, thus it is a civilian organisation. I still hold the view that the sarin released by the cult was equally harmful as sarin which was made by (or for) the military.

While I wrote yesterday about nerve agents which have traditionally been viewed as military weapons only, I am aware that there are some substances which have very similar effects on humans and animals which have uses in civilian life. It is also interesting that “Chemistry in the Market Place” (I am not totally sure if it is that book or another one from the same era) made the claim in the 1980s that the Germans experimented with sarin in a vineyard. The Germans found that it exterminated all the insects in the vine yard but every accident which workers had was fatal.

If it is true this attempt at using sarin as a agricultural pesticide does slightly change the “military only” status of sarin a little further.

I would advise people to keep an open mind regarding what the poison was and where it came from. I hold the view that Russia does not have a monopoly on making the vile abomination known as “nerve gas”, the problem is that people in other places know how to do it and in some cases have gone and done it.

I do not know who was responsible for releasing the structure of VX to the general public, years ago when I was in Aberdeen (Scotland) I randomly chanced on the article by Dr Yang and I recall asking myself the question of “was it a good idea to tell the scientific community what the structure of VX is ?”.

One of the problems we have in our current age is the management of information, I have encountered people who have got it wrong equally from both extremes. There are some people who think it is proper and right that no information on some topics should be released into the public domain. Some years ago I read with interest an article in Chemistry World on the subject of “fracking” which wrote about “chemicals” being injected into fracking wells to stimulate the production of gas. The problem in my mind is that some substances either injected or recovered from a oil or gas well are quite harmless while others are harmful to humans, animals, plants, bacteria or other life forms. The failure to discuss openly the question of “what is going into and out of the well” does inhibit a honest and reasonable debate about “fracking”.

Equally wrong is the “pirate party” / wikileaks types who think that they have a right or even duty to release all and any information into the public domain without considering the results of releasing the information. These people seem to hold the view that “everone should know everything about everone” and that no restrictions or controls should exist on intellectual property. Commonly the pirate party people think that they should be able to get music for free and watch feature films for free, but their views are harmful to many sectors.

The problem is that some information does have misuse potential, how about.

  1. How many armed guards will the king of Sweden have with him on Tuesday afternoon and where will be spending the afternoon.
  2. How many 999 calls can be handled at once in London at any one time.
  3. What make / model of safe is used at a hospital pharmacy to store a large amount of diamorphine (heroin)
  4. What is the location of a shelter for battered women who are fleeing from a violent partner or ex-partner.
  5. How much gold is stored in a jewelry workshop over the weekend.

Now I suspect that the vast majority of my readers are decent people who if they chanced upon one of these bits of information would not misuse it. Some of them might even be so publicly spirited to report the security leak

In the interests of public safety I will not be telling you how to do it or answering some other questions. You are free to ask me questions via a comment on this blog, but keep in mind that I will refuse to answer some questions on this topic.

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