Naked Science Forum
Non Life Sciences => Chemistry => Topic started by: Anarchistkid on 03/03/2008 02:23:18
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So this chemical weapon "Sulfur Mustard" i know theres a few forms of it and it causes blisters and all that but what is the absolute worst form?
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I remember reading somewhere about mustard gas mixtures, but it was some time ago, and I cannot find it right now.
One of the things one has to ask is what do you mean by "the absolute worst form". The thing you have to remember about chemical agents is that they each have different characteristics, and what might be very effective in one context may be almost useless in another context. Sometimes you use mixtures of chemicals when one chemical does not have exactly the effect you want, or to improve the stability of the chemical so it does not break down so easily, or to make it easier to spread the chemical (e.g. make it easier to turn into an aerosol).
The first thing about mustard gas was that early versions of it were fairly impure, so efforts were made to improve its purity (pure mustard gas is anyway orderless, and it was the impurities that gave it the mustard smell).
One of the things about mustard gas, apart from the fact that in its purest form it is orderless, is that the first effects of it may not be felt for around 4 hours (in smaller doses, maybe not for 24 hours). Depending on what you are trying to do, this may be what you want, or it may not be what you want. If you want to create massive panic, then a gas that the enemy cannot detect for 4 hours may not be what you want; but if you want to cause the maximum number of casualties, then having people breathing it in, and having it on their skin, for 4 hours or more before they realise they have been poisoned (by which time it may be too late to treat them) will mean far more people will be exposed to the chemical because they would not have raised the alarm because they did not realise it was there (this is very different from something like sarin, which is a nerve gas that has very quick effects, and can cause panic quickly amongst the enemy, but it also means that the enemy can quickly protect themselves against it as soon as the first troops start falling victim). Sometimes mustard gas (which is, like most chemical weapons, actually an aerosol rather than a gas) would be mixed with other chemicals to have a quicker effect.
The other thing about mustard gas is that it would linger in the area for a long time. This is fine if you just want to clear an area so that it becomes uninhabitable, but becomes a problem if your own troops want to occupy the area after the enemy has left, because your own troops could be exposed to the chemical when they moved into the enemy position. For that reason, sometimes chemicals that were less stable, or more easily blown away by the wind, could sometimes be better if you wanted your own troops to move into the area where the chemical was used.
One final point is that in warfare the object is not always simply to kill the enemy (and often the use of chemical weapons was more to cause injury than to cause death). It is said that if you kill one enemy soldier, you have removed one enemy soldier from the battlefield; but if you injure an enemy soldier, then you have removed at least three enemy soldiers from the battlefield, the one that you have injured, and at least two of his comrades who now be busy trying to give their injured comrade assistance.
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OK, some links that might be pertinent.
Firstly, there were apparently experiments with combining mustard gas with anthrax spores (how much more nasty can you get than that), but it was never weaponised.
http://www.cbwinfo.com/Chemical/Blister/HD.shtml
In 1942, research undertaken under the auspices of the M-1000 Committee of the Canadian National Research Council established that anthrax spores could survive in sulfur mustard. The research had been undertaken with the goal of developing a combined biological and chemical weapon, the idea being that the blisters caused by the mustard agent would facilitate infection by the anthrax. The program was terminated without proceeding to weaponization.
From the same web site:
http://www.cbwinfo.com/Chemical/Blister/HD.shtml
By July, the Germans had accumulated enough of the new agent to use it, and on the evening of July 12, 1917 they carried out a bombardment of British troops near Ypres, Belgium. Because of the latent period before the effects of mustard make themselves apparent, the men in many gases didn't realize they were being gassed, or thought that the agent was not very effective. This impression was corrected within a few hours, as the latent period ended.
The effects of the attacks with sulfur mustard were overwhelming. In the first week in which the Germans employed the agent, the British would admit 2934 mustard gas casualties to their various medical units - units which had been treating around 350 gas casualties a week in the period leading up to the attack. In the first three weeks in which the Germans employed their new agent the British would suffer 14,296 gas casualties.
While the German expectations for its lethality were not borne out (only a bit more than 2% of mustard casualties were fatalities, which should be compared to about 8% for casualties from rifle fire), its effects were certainly not disappointing in the military sense. Indeed, had it been more lethal, it might have been less damaging. The need to care for mustard gas casualties placed burdens on the supply and medical systems that would not have been produced by fatalities. At the same time, the nature of the injuries it inflicted - the potential for blindness, the disfiguring and slow-healing lesions of the skin, and the rather painful death of those who had inhaled significant amounts - produced a strongly negative effect on the soldiers who had to suffer attacks using it.
Nor did it help that gas masks provided only a partial protection against this new agent - a man wearing a mask could still suffer incapacitating burns if his skin was exposed. The uniforms of the period could absorb the agent while someone was passing through a contaminated area, and carry contamination to others while the original victim was still unaware of exposure.
Note the comment that people exposed to mustard gas could carry the gas with them without realising it. This was also a problem with victims of the gas - if the victim was not properly decontaminated before being passed into medical care, he could actually cause harm to the doctors treating him, since he could be carrying the chemical on his clothing and skin.
http://www.opcw.org/resp/html/mustard.html
At room temperature, mustard agent is a liquid with low volatility and is very stable during storage. The melting-point for pure mustard agent is 14.4 oC. In order to be able to effectively use mustard agent at lower temperatures, it has been mixed with lewisite in some types of ammunition in a ratio of 2:3. This mixture has a freezing-point of -26 oC. During the Second World War, a form of mustard agent with high viscosity was manufactured by means of the addition of a polymer. This is the first known example of a thickened CW agent.
It shows how mixtures were used not so much because it increased its toxicity, but because it made it usable in environments where otherwise it would not be usable (e.g. in very cold weather). The thickening agent would have made the gas linger longer, so making it useful where you did not want to allow the enemy back into an area (but similarly you would have had difficulty entering the area also).
Also from the same site:
http://www.opcw.org/resp/html/mustard.html
Incidents are still occurring annually in the neighbourhood of Sweden where people risk injury from mustard agent. This largely involves fishermen who are exposed to mustard agent brought to the surface by fishing nets. The background is found in the dumping of chemical weapons after the Second World War in waters off the Danish and Swedish coasts. Many fishing ports in south Sweden and Denmark have resources to care for injured people and to decontaminate equipment contaminated by mustard agent. Certain resources are also available on the fishing vessels.
Mustard agent is very simple to manufacture and can therefore be a "first choice" when a country decides to build up a capacity for chemical warfare.
Apart from mustard agent, there are also several other closely related compounds which have been used as chemical weapons. During the 1930's, several reports were published on the synthesis of nitrogen mustard agent and its remarkable blistering effect. The mechanism of action and symptoms largely agree with those described for mustard agent. Germans and Americans started the military production of nitrogen mustard agent in 1941 and 1943, respectively, whereas the development in England was abandoned following an explosion. There is no verified use of nitrogen mustard agents as chemical weapons and their usefulness is restricted by these types of agents being unsuitable for storage.
The comment about nitrogen mustard there refers to a later variant of mustard gas, but is also the bases for one of the first anti-cancer drugs, and other medical purposes - it is an example of the old adage that the the key aspect of a poison is dosage, and any drug is just a poison in the right dosage and administered in the right way.
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http://en.wikipedia.org/wiki/Tris%282-chloroethyl%29amine
Tris(2-chloroethyl)ethylamine is the organic compound with the formula N(CH2CH2Cl)3. Often abbreviated HN3, it is a powerful blister agent and a so-called nitrogen mustard gas (it is not a gas) used for chemical warfare. HN-3 was the last of the nitrogen mustard agents developed. It was designed as a military agent and is the only one of the nitrogen mustards that is still used for military purposes. It is the principal representative of the nitrogen mustards because its vesicant properties are almost equal to those of HD.
Mode of action
Nitrogen mustards react via an initial cyclization to the corresponding iminium salt. The rate of this reaction is pH dependent because the protonated amine cannot cyclize.
Applications
HN-3 has found some applications in chemotherapy, e.g. for Hodgkin's disease, but it is mainly of interest for its military uses and is the only one of these agents that remains anywhere as a military agent. These agents are more immediately toxic than the sulfur mustards.