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Author: Subject: Idea for making haloalkanes from OTC ingredients?
Cou
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[*] posted on 24-4-2019 at 12:54
Idea for making haloalkanes from OTC ingredients?


i've never done any of these reactions in a lab, in practice etc.

1: acid catalyzed dehydration of ethanol w/ sulfuric acid to ethene (would have to be captured in a balloon)

2: hydrobromination to 1-bromoethane (i guess you would somehow mix ethene gas and gaseous HBr in a flask)

[Edited on 24-4-2019 by Cou]
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Pumukli
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[*] posted on 24-4-2019 at 21:06


1., It is OK, you can find the actual recipe for making ethylene in various online posted old org. chem. preparative lab. manuals.

2., I don't remember seeing this reaction in the above mentioned books, but my brain can fail me on this one. I do, however, saw the Br2 addition reaction either with or without water, yielding either 1,2-dibromo-ethane or 2-bromo-ethanol - with good yields. (Unfortunately both of these compounds are known industrial carcinogenes, so careful with them!)

3., If I wanted ethylbromide (low bp compound, with all the associated problems of handling!), I would start from ethanol, alkali-bromide salt and sulfuric acid. Should I mention that ethylbromide is also a nasty carcinogene?

[Edited on 25-4-2019 by Pumukli]
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chemplayer...
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[*] posted on 25-4-2019 at 20:24


There are two ways we've played with for iodides (typically the most reactive of the haloalkanes):

1. The well documented way which is to react an alkali metal iodide salt (e.g. KI) together with the relevant alcohol and with 85% phosphoric acid. The mixture is heated and distilled and the iodide (typically quite volatile) comes off. The reaction takes a long time though for good yields and you've got to be patient. This is on video in our archive.

2. If you've got solid iodine then mixing aluminium foil, the solid iodine, and an excess of the alcohol (anhydrous), and allowing this to react will also produce alkyl iodides in differing yields. For us it worked best with ethanol, then not quite so well for methanol, and then lesser yields for higher alcohols. How it works we're not totally sure (there are a number of theories and ideas), but you do have to be careful as the reaction between iodine and aluminium metal (or with aluminium metal and the alcohol) can become quite vigorous. Again, a lot of patience (3-4 hours) is required. Again, we did a few videos testing this out.

As other commentators have rightly pointed out, take care with these compounds as they are insidiously toxic.




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ninhydric1
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[*] posted on 25-4-2019 at 20:35


If you distill the bromoethane as you form it (in a well-ventilated area) and put some water in your receiving flask, allowing the alkyl halide to sink to the bottom, you pretty much entirely eliminate vapor issues (assuming your distillation apparatus is airtight).

You can also form dihalides from ethers as well. I've synthesized 1,4-dibromobutane from THF and H2SO4/NaBr, then steam distilled it from the reaction mixture.




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draculic acid69
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[*] posted on 25-4-2019 at 23:57



You can also form dihalides from ethers as well. I've synthesized 1,4-dibromobutane from THF and H2SO4/NaBr, then steam distilled it from the reaction mixture.

Can you please share how you did the 1,4dibromobutane ie: ratios/reaction times,any tips to a higher yeilds.
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CobaltChloride
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[*] posted on 26-4-2019 at 15:40


The most simple OTC synthesis of a haloalkane is that of MeI posted here I'd say.
https://www.sciencemadness.org/whisper/viewthread.php?tid=65...
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draculic acid69
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[*] posted on 26-4-2019 at 23:41


Am I right in thinking that 2 mol h2so4 and 2mol NaBr to 1 mol thf refluxed for however long will equal 1,4dibromobutane? Any one know how long or what temperature to do this at?
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