A base, in chemistry, refers to any substance that releases hydroxide ions (OH−) when dissolved in water or aqueous solution. Many bases, however, don’t readily carry hydroxide ions but they too produce high levels of OH− when treated with water. This type of reaction can be observed when ammonia is treated with water to produce ammonium and hydroxide.
Bases also have distinctive physical characteristics too, for example, they are bitter in taste (acids are sour) and gives a slippery sensation when touched. Bases as a whole are important and are a key ingredient in certain industries. They are used to make paper, soap and synthetic rayon, bleaching powder, antacid, etc. While they are generally considered as the chemical opposite of acids, there are few known acids which can behave just like bases under certain circumstances.
Just like acids, bases can also be either strong or weak. A strong base is simply a chemical compound that breaks apart (dissociate) completely into water and yield hydroxide ion. Common examples of strong bases are NaOH (Sodium hydroxide) and Ca(OH)2 (Calcium hydroxide). Whereas, a weak base dissociates into the water only to a certain degree.
Superbase: Superbase(s) are powerful chemical compounds that have an extremely high affinity for protons and are stronger than hydrogen ion. Superbases are used to carry organic synthesis and are an important component of the physical organic chemistry.
The term superbase is, however, not new and has been used for more than one and half a century. Since superbases are susceptible to a violent reaction when coming in contact with either water or carbon dioxide, a special solvent is required to carry chemical reactions involving superbases. Superbases can be classified into three types; organic, inorganic and organometallic. Below, is a list of 10 strongest bases on the Earth.
10. Lithium Hydroxide
Chemical Formula: LiOH
First in the list is lithium hydroxide, a white crystalline substance (in anhydrous form) with high water solubility level and corrosive nature. It’s also the weakest of all known alkali metal hydroxides. Lithium hydroxide is produced by inducing a reaction between calcium hydroxide and lithium carbonate in a salt metathesis reaction.
Li2CO3 + Ca(OH)2 → 2 LiOH + CaCO3
A large amount of LiOH is used to manufacture lithium soaps. Another important use of lithium hydroxide is done in ventilation systems of submarines and spacecraft to cancel out carbon dioxide by creating water and lithium carbonate.
2 LiOH + CO2 → Li2CO3 + H2O
It is also used as a corrosion control measure in nuclear reactors (pressurized water reactor) and as a battery electrolyte.
9. Sodium Hydroxide
A working model of Chloralkali process or Chloralkali electrolysis
Chemical Formula: NaOH
Sodium hydroxide, popularly known as caustic soda is an ionic compound that carries sodium cations Na+ and hydroxide anions OH–. NaOH is known for its extremely corrosive nature, especially in room temperature as it can easily decompose proteins. It is capable of attracting (absorbing) CO2 and moisture from the air.
Sodium hydroxide is largely used for chemical pulping in the paper industry. Its other applications include soaps and detergents manufacturing, raw food processing, cement manufacturing and in water treatment facilities to neutralize the pH values of water. It is also used in petroleum industry time to time in order to neutralize acids and increase alkalinity levels of a certain solution.
In ancient times, NaOH was produced by treating calcium hydroxide with sodium carbonate. By the 19th century, it was replaced by Solvay process, which was actually used to produce sodium carbonate, a cheap alternative to NaOH. Today, most of the industrial sodium hydroxide is produced through chloralkali process.
8. Potassium Hydroxide
Chemical Formula: KOH
Many of you may recognize potassium hydroxide as caustic potash, a solid white substance which is known for its highly corrosive nature. Similar to sodium hydroxide, KOH is colorless (commercially available in white) and strong quintessential base.
While potassium hydroxide and sodium hydroxide can be used interchangeably for various purposes, most industries use NaOH since it’s the cheaper of the two. Anyway, it is used to produce bio-diesel, manufacture soaps and as an electrolyte in some batteries.
Pure potassium hydroxide is produced by reacting sodium hydroxide with degraded or impure potassium. The chemical compound is potentially hazardous and causes skin burns when the concentration is more 2%. Anything between 0.5% to 2% can cause severe irritations.
7. Lithium bis(trimethylsilyl)amide
Chemical Formula: C6H18LiNSi2
Lithium bis(trimethylsilyl)amide or LiHMDS for short, is a non-nucleophilic superbase, which has important applications in laboratories. Like other lithium bases reagents, it can form cyclic compounds with trimer, an anion created by a combination of three ions of the same substance. LiHMDS is usually prepared by reacting bis(trimethylsilyl)amine with butyllithium.
HN(SiMe3)2 + C4H9Li → LiN(SiMe3)2 + C4H10
6. Sodium Hydride
Chemical Formula: NaH
Sodium hydride belongs to a special group of hydrides known as saline/ionic hydrides (composed of Na+ and H− ions), which exists in salt-like form, unlike ammonia and water. It’s largely used as a base in organic synthesis, though few insignificant uses of NaH are also known. Sodium hydride is produced by reacting hydrogen with liquid sodium.
Pure sodium hydride is colorless, but commercial samples can appear grey. Furthermore, NaH is about 40% denser than its precursor chemical compound sodium.
In rare cases, the compound can take the form of ‘inverse sodium hydride’, where sodium and hydrogen ion swap charges (Na− and H+). Na− is an alkalide, which makes this compound more energetic than the standard sodium hydroxide (due to the increased net displacement between the two electrons).
NaH is pyrophoric in nature. It also reacts violently with water and produces sodium hydroxide, a corrosive substance, when goes through hydrolysis.
5. Sodium Amide
Chemical Formula: NaNH2
Sodium azanide, sometimes known as sodium amide is one of the strongest known bases in the world. It’s an important, commercially available chemical compound which is generally used in organic synthesis. NaNH2 conducts electricity (in a fused state) since its electrical conductance properties are almost similar to that of sodium hydroxide.
While pure sodium hydroxide is usually white, most of the commercially available NaNH2 is grey in color due to the presence of impurities in form of metallic iron. Usually, sodium amide is prepared by reacting ammonia gas with sodium.
2 Na + 2 NH3 → 2 NaNH2 + H2
Sodium amide is preferred in certain types of synthesis due to its functions as a nucleophile. It’s a potentially dangerous chemical substance, which must be handled with extreme caution. It can react vigorously with water, especially when present in solid form
4. Lithium diisopropylamide
Chemical Formula: C6H14LiN
Next on the list is Lithium diisopropylamide, another non-nucleophilic superbase which is known for its highly corrosive nature and solubility. Under normal conditions, the compound is synthesized by treating cooled diisopropylamine solution (tetrahydrofuran) with butyllithium. Needless to say, lithium diisopropylamide is corrosive and pyrophoric but commercial solution are much safer.
Image Courtesy: Rockwood Lithium
Chemical Formula: C4H9Li
n-Butyllithium or n-BuLi for short is a commercially important superbase, mostly used as a catalyst for polymerization in order to produce synthetic rubber. It has uses in the pharmaceutical industry as well. Although Butyllithium is mostly colorless, it can go through mild color changes either when comes in contact with alkanes or when they age.
Apart from being a superbase, n-BuLi is a powerful reducing agent as well as nucleophile (chemical that donates an electron pair to form a bond). Butyllithium is generally produced by reacting lithium with either 1-bromobutane or 1-Chlorobutane.
2 Li + C4H9X → C4H9Li + LiX
Butyllithium is unstable and can react vigorously with water and carbon dioxide, but it can be stored safely under inert gas.
2. Lithium monoxide anion
Chemical Formula: LiO−
Epa: 1782 kJ/mol−1
Lithium monoxide anion was once the world’s strongest base before it was dethroned in 2008. Like other superbases, lithium monoxide is prepared in an aprotic solvent and is also known for its extremely corrosive nature.
Synthesis of lithium monoxide anion is a complex procedure and is difficult to carry out in a controlled manner. Usually, a small amount of lithium oxalate (Li2C2O4) is used as the precursor, which goes through the electrospray ionization process. The resulted compound lithium oxalate anion (LiC2O4) is isolated and then processed with collision Induced dissociation twice.
As a result, we get Lithium monoxide anion (LiO−) and a Carbon dioxide molecule. There is no known use of lithium monoxide anion.
1. ortho-Diethynylbenzene dianion
Preparation of o-diethynylbezene dianion
Chemical Formula: [C6H4(C2)2]2−
Epa: 1843 kJ/mol
ortho-Diethynylbenzene dianion is perhaps the strongest base known to us. It was initially synthesized/discovered by a group of researchers in Australia using mass spectrometry.
Like other superbases, ortho-diethynylbenzene dianion can only be kept in gaseous phase. This, however, provide an ideal environment to measure its basicity levels with greater precision. Calculations have shown that ortho-diethynylbenzene dianion has a proton affinity of 1843 kJ/ mol−1 far more than that of hydroxide (1,633.14 kJ/mol).
Furthermore, ortho-diethynylbenzene dianion has two isomers (with same molecular formula, but different chemical structure); Meta-diethynylbenzene dianion and Para-diethynylbenzene dianion, second and third strongest base ever synthesized. Both the isomers including ortho-Diethynylbenzene dianion have no known use and exist in the gaseous state.