Synthesis

Salts are mixtures of charged species, or ions. They have an avid tendency to remain solid due to the strong interactions between their charged components. About a hundred years ago, people started noticing certain compounds that were ionic would nonetheless melt below or around room temperature. This is a unique class of liquid - extremely polar, and capable of dissolving lots of odd stuff. They also tend not to evaporate very easily, the ionic interactions between components of the salt being so strong. For these reasons, a lot of people have suggested they could be used in "green chemistry…
One of my best friends in undergrad, upon learning about the use of acetal protecting groups for carbonyls, exclaimed, "they're like ketone condoms!" Indeed. Protecting groups are ubiquitous in organic synthesis, and another one you see all the time is Boc, which is used to protect amines: Boc2O, or "boc anhydride," is one of my favorites. Using it on your amine will yield a "boc protected amine." Upon acid deprotection, it yields the parent amine, carbon dioxide, and t-butylene. The latter two are both gases, which gives about as easy a cleanup as you could hope for (that's the problem with…
There are a number of "strong" acids that are essentially completely dissociated in water - hydrochloric and sulfuric acid are two of the most common. Unfortunately, these are often volatile (as in HCl), insoluble, or otherwise ill-behaved in organic solvents. The organic sulfonic acids are quite strong - the functional group is essentially sulfuric acid with one of its valences occupied by a carbon functional group instead of another -OH. para-toluenesulfonic acid, or tosylic acid is probably the most common sulfonic acid used in the lab. Much stronger than carboxylic acids (the other…
The fluoride ion is important to synthetic chemistry, often because it can be used to cleave silyl ethers (the silicon analogue of a carbon ether). Fluoride is notorious for holding onto water (like any tiny ion - lithium is about as bad), so even an "anhydrous" solution of TBAF in (say) THF will often contain ca 5% water. The less water you have, the more "naked" fluoride anion you have, which is much, much more reactive than aquated fluoride.
Normally, iodine just makes one bond, as you'd expect from a halogen. Some compounds, though, force it into lively higher oxidation states (hopefully without the tendency to explode, as some highly oxidized iodine reagents worryingly exhibit). There is a whole field of "hypervalent iodine" chemistry. A major use is to get something that is a good oxidizing agent, soluble in organic solvent, and milder than the time-honored usual suspects: things like permanganate or dichromate, which work a treat, but often too well, chewing your stuff up a bit more than you'd like. I (V) reagents tend to be…
Iodine week continues with IPBC, or 3-iodo-2-propynyl-N-butylcarbamate, a fungicide: IPBC has been around for ages, but you see it more and more in cosmetic products. That "iodopropynyl" part, where the iodine is bound to the triply-bonded carbon, is a very reactive functional group. IPBC has been implicated as a cause of dermatitis (but fairly rarely). Certain compounds can induce an immune reaction after repeated exposure. These are called sensitizers. At the levels you find them in consumer products, the worst you're likely to get is a rash (although not always). In the lab, we're usually…
Methyl iodide is another simple organoiodide: Probably the most common lab use is tacking a methyl group onto something; MeI is a great substrate for the SN2 reaction. Despite its ubiquity, methyl iodide isn't nearly the best alkylating agent. It's cheap and simple, so it sees a lot of use, but there are many things that are better, such as dimethyl sulfate (used a lot industrially, from what I've read), methyl triflate (PDF) (toxic and great), trimethyloxonium salts (my favorite), and the so-called "magic methyl," methyl fluorosulfonate, which has a pretty good vapor pressure (being…
Here is another molecule that's gone out of favor in recent decades: carbon tetrachloride: Chlorinated solvents are great solvents. Something about the polarizability, medium polarity, (relative) lack of reactivity, just makes them the only thing that will work in a lot of applications. The three simplest chlorinated solvents are dichloromethane, chloroform, and carbon tetrachloride. Those are CH2Cl2, CHCl3, and CCl4. Those are in order of increasing degree of halogenation, and, coincidentally, increasing degree of toxicity. Methylene chloride/dichloromethane is regarded as a necessary evil…
This is one that will be familiar to anyone who works in chemistry, but I was a bit surprised to see it the first time I went into a lab. Certain compounds, called esters, can be prepared from an acid and an alcohol (usually a carboxylic acid). They are ubiquitous in the flavor and fragrance industry (although they're not quite stable to water over the long-term, and once an ester is hydrolyzed, it liberates its component alcohol and acid, which are often pretty rank). One classic organic lab is preparing some sweet-smelling esters from otherwise nasty-smelling carboxylic acids and esters (…
Yesterday's entry on crown ethers demonstrated a way to do reactions with a mixture of polar and nonpolar substrates. These crowns allowed for ions to be brought into the nonpolar solvent. Another approach is to just throw up your hands and mix oil and water, so to speak: reactions can occur with two phases. Not very well, though. One way to help this along is with phase transfer catalysts, usually quaternary ammonium salts. A QAC, ammonium compound, quat, or whatever you want to call it has four substitents on the nitrogen, (nitrogen usually carries 3) so it has a positive charge. This makes…