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Author: Subject: Useful and versatile substrates and reagents
Lambda-Eyde
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[*] posted on 20-10-2013 at 20:00
Useful and versatile substrates and reagents


As amateur chemists our projects are limited by the availability and prices of compounds, and to a lesser extent, their hazards. Amateur organic syntheses often start out with very simple substrates and often even the reagents used to afford complex transformations are made from the ground up, unlike in a professional setting where highly modified benzenes, amines, alkenes and complex palladium catalysts are bought pre-made and ready for use. Due to these facts, amateur chemistry tends to revolve around the starting point, and not the finished product. As home chemists we often pick our projects by asking "what interesting can I make from this readily available compound?" instead of "how do I make natural product X?" The answer to the latter question is found in academic journals where one almost certainly will find that a substrate or reagent is out of reach and thus make one forget about the project before starting. Even with access to professional suppliers a complex diene will probably cost too much to make it worth it, and some will even feel that it's akin to cheating. After all, part of the appeal of amateur chemistry is to get by with materials that can be easily sourced for most people.

From an amateur's perspective it is therefore desirable to buy compounds that are (1) cheap, (2) not easily made in bulk from simpler materials with the means available to the home chemist and, (3) versatile - that is, they have several applications, are used in a wide range of useful/powerful transformations or serve as a backbone or starting point for several interesting molecules. Which is the point of this thread: Share with us one compound that fulfills these criteria to help people build their home labs, and inspire them to do interesting projects to share with the rest of us!


Some guidelines for posting:

  • Recommend a compound that fulfills the above criteria

  • The compund shouldn't be too obvious - everyone knows that sulfuric acid is good to have on hand

  • If possible, provide a source for the compound

  • Describe what the compound can be used for, preferably with links for further reading (Wikipedia, papers, threads etc.)

  • People love images. Provide structural formulas, pictures, reaction schemes where it makes sense.

  • If there are any appreciable dangers associated with the compound, be sure to mention them





My recommended compound is:


Phthalic anhydride







Phthalic anhydride is the anhydride of o-phthalic acid. The corresponding acid, o-phthalic acid (not to be confused with its isomers) dehydrates readily to the anhydride on heating due to the thermodynamically favorable formation of a 5-membered ring.

Although it's not the focus of this thread, phthalic anhydride is readily made from oxidation of naphthalene or o-xylene with potassium permanganate, or from its esters which are used as plasticizers in PVC gloves among other things. These routes have been extensively discussed in the forum [1] [2] [3]. Our own UnintentionalChaos (of Youtube fame) has documented both the xylene oxidation [4] and the plasticizer extraction [5].

Phthalic anhydride shows up on eBay very often, which is where I bought mine - I paid around 15-20$ for 500 g in a sealed Aldrich bottle. NB! At least one member has received phthalic acid when he thought he was buying the anhydride. If you're not buying a sealed bottle from a reputable supplier, taking a melting point is advised. Thankfully, converting the acid to the anhydride is very easy, as already mentioned. Elemental Scientific also has it in stock in various package sizes.


Why it's so damn useful:

Phthalic anhydride is the starting point for a lot of interesting stuff:


It is a few steps away from luminol, the anhydride is first nitrated to yield 3-nitrophthalic acid which is then reacted with hydrazine. Finally the nitro group is reduced to an amine to yield luminol.


Heating with resorcinol and zinc chloride affords the fluorescent dye fluorescein.


Via esterification, it can be used to resolve chiral alcohols using chiral amino acids.


Upon heating with concentrated ammonia or ammonium carbonate, it forms phthalimide in excellent yield. [OrgSyn] I recently performed this synthesis myself and will probably write a thread in prepub on it when time allows. Phthalimide is another versatile compound and is among other things used in the Gabriel synthesis which is a powerful reaction for producing primary amines.


Phthalimide can also be used in the synthesis of phthalocyanine, an intensely colored dye which forms complexes with a lot of metals. Phthalocyanine can also be made directly from phthalic anhydride and urea.




Phthalic anhydride or phthalimide can also be used in the synthesis of anthranilic acid, which opens up a lot of interesting chemistry, for example benzyne reactions. Via the Sandmeyer reaction, the amine moiety can be swapped for iodine, which leads to the synthesis of IBX or the related Dess-Martin periodinane, a class of mild oxidants which are useful to the more advanced organic chemist.





That's all I can think of, but there's probably more. Do you have a similar compound to recommend?

[Edited on 21-10-2013 by Lambda-Eyde]




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[*] posted on 20-10-2013 at 23:42
sodium nitrite


This is a very versatile reagent, which allows one to perform many interesting chemistry experiments, and it is useful in many syntheses as well. It is relatively cheap and is not that hard to find. It appears on eBay quite often and that is where I obtained it as well.

At the moment of writing, two sellers for EU-locations:

http://www.ebay.nl/itm/1kg-Sodium-nitrite-high-quality-/3208...
http://www.ebay.nl/itm/SODIUM-NITRITE-NaNO2-250-G-PURTY-98-5...

Sometimes, curing salt is sold on eBay as well. Be careful with that, it is not always pure NaNO2. Sometimes it is just NaCl with a small percentage of NaNO2 in it. The two links above, however, are nearly pure NaNO2.

Sodium nitrite is a lovely source for making NO and N2O3 (mix of NO and NO2).

Mix it with acidified FeSO4 and you get nearly pure NO. Mix it with any dilute strong acid and (optionally) heat a little and you get NO+NO2 mix. These gases can be used in quite a few other experiments. For people who cannot obtain nitric acid, but who can obtain dilute HCl or H2SO4 this opens up a way of making nitric acid at home.

With many alcohols you can make the interesting nitrite esters. Be careful with these, avoid inhaling them, because in some people they give very nasty headaches. These nitrite esters can be interesting starting points for making azides, when combined with hydrazine or salts of hydrazine. The gaseous esters methylnitrite and ethylnitrite are especially easily made, simply add some NaNO2 to a solution of (m)ethanol in dilute H2SO4. The gas bubbles out of the solution.

Nitrite gives rise to complex-formation with a lot of transition metal compounds. E.g. with cobalt ions it forms the interesting hexanitrito-complex under certain conditions, with copper it also forms interesting complexes at low pH. With iron at low pH it forms complexes in which the iron has oxidation state +1 (which is very special for iron).

With concentrated sulphuric acid you can make a solution of nitrosyl (bi)sulfate, simply by adding solid NaNO2 to cold conc. H2SO4 and dissolving it. Nitrosyl sulfate, (NO)2SO4 or NO-HSO4 is an interesting reagent, both in organics and in inorganic chemistry.

Some other reagents, which are easily made with NaNO2:
- ONBr in the gas state
- ONCl, dissolved in conc. HCl
- NOClO4 if you have conc. HClO4

Finally, I want to mention the formation of azo-compounds with nitrite. Some of these are very interesting and are on the basis of a whole class of dyes with bright colors.




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[*] posted on 21-10-2013 at 10:15


I propose cyclohexanone which I am source too.
Here an image:

http://imageshack.us/photo/my-images/20/gvno.jpg/

It's very useful and versatile. It has a role as catalyst in decarboxylation of aminoacid, tryptophan for example, whereas in this forum there is an open discussion.
Another use is as precursor for many dissociative, although, it is not a watched chemical ( in Europe ).
Adipic acid can be synthesized by treating cyclohexanone with 65% nitric acid.
Since it is a ketone, it could be condensed through aldol reactions.
And cycloexylamine obtained after imine formation and reduction by reflux of formic acid \ ammonium formiate solution of the said ketone.

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[*] posted on 21-10-2013 at 11:54


Woelen: I've found quite pure sodium nitrite in stores catering to meat/fish curing(as you alluded to.) I've also had no trouble getting small amounts from the local butchery.

I did an interesting experiment a few days ago, mixing hydrochloric acid with potassium nitrate in a small beaker, which was placed inside a larger beaker on a bed of aqueous(roughly 35%) sodium hydroxide. I then dropped a bunch of copper wire in the pseudo-aqua regia mix, and quickly placed a jar inverted over the beaker, forming an air tight seal due to the water layer in the larger beaker. Brown fumes came off and solvated in the aqueous NaOH, when the fumes stopped evolving I evaporated the outer beaker. until non-crystalline precipitate started forming(NaNO3 forms distinctive large crystals.) then decanted the rest of the liquid into an evaporation tray to get very small white/off white crystals. Addition of HCl to the precipitate results in a lot of brown noxious gas so I assume its NaNO2.

The idea was initially from Nurdrage's HNO3 preparation on youtube, using NaOH(aq) instead of H2O to solvate the NO/NO2.

I have no idea what the residual green solution in the small beaker is... Half way through evaporating it, it turned dark brown and glassy.






EDIT:
To stay in line with the spirit of the thread, I find plain carbon to be extremely useful. It's near impossible to get some of the more reactive metals(Na, K, Ca, etc.) over here. A thermite mix of W + KNO3 with a closed(but not fixed) carbon crucible on top containing any of the aforementioned metal's oxides has yet to fail me. I often find tiny pieces of potassium in the recovered thermite melt as well though, which is kinda odd.

[Edited on 21-10-2013 by Mesa]

[Edited on 21-10-2013 by Mesa]
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