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Key Chemicals Month
This month we feature chemicals that have important applications in industry and the lab.—Ed.
Calcium carbonate (CaCO3) is a natural product found in many settings, including the minerals aragonite1 and calcite2; the sedimentary rocks limestone3 and chalk4; and animal structures such as eggshells, shellfish exoskeletons, and pearls. CaCO3 began to appear in the chemical literature in 1878, on topics ranging from the essential oil of sage to nitrification in soil to citric acid in unripe mulberries.
A fourth article from 1878, however, dealt with the chemistry of CaCO3 and other inorganic compounds. M. M. Pattison Muir at the University of Cambridge (UK) wrote about “the influence exerted by time and mass in certain reactions in which insoluble salts are produced”—an early treatise on equilibrium and what soon after became known as Le Chatelier’s principle.
Almost all CaCO3 used in industry and research comes from natural sources, but the pure compound also can be prepared by passing carbon dioxide through an aqueous solution of calcium hydroxide or calcium chloride. CaCO3 has a vast number of practical uses, the major ones can be categorized as follows:
- Construction products (building materials, road-paving aggregate)
- Ingredient in manufactured materials (paint, rubber, plastics, ceramics, inks, adhesives)
- Ingredient in consumer products (foods, cosmetics, pharmaceuticals)
- Filtering agent (oil, wine, and sugar)
An interesting slant on CaCO3 in nature was reported in 2011 by Daniel I. Speiser* and Sönke Johnsen at Duke University (Durham, NC) and Douglas J. Eernisse at California State University, Fullerton. They examined the ocelli (simple eyes) in the chiton (marine mollusc) Acanthopleura granulata to determine whether the eyes provide the mollusc with spatial vision. Although almost all biological lenses are composed of proteins, the researchers discovered that A. granulata‘s lenses are made of aragonite. When they assessed the animal’s vision, they found that the ocelli “see” with an angular resolution of ≈9–12º.
1. CAS Reg. No. 14791-73-2; orthorhombic crystal structure.
2. CAS Reg. No. 13397-26-7; rhombohedral crystal structure.
3. CAS Reg. No. 1317-65-3.
4. CAS Reg. No. 13397-25-6.
Calcium carbonate hazard information*
| Hazard class** | GHS code and hazard statement |
|---|---|
| Short-term (acute) aquatic hazard, category 3 | H402—Harmful to aquatic life |
*Most safety data sheets state “not a hazardous substance or mixture” or similar wording.
**Globally Harmonized System (GHS) of Classification and Labeling of Chemicals. Explanation of pictograms.
Molecules from the Journals
In 1997, in a search for more reactive dienes with which to conduct Diels–Alder cycloadditions, Sergey A. Kozmin and Viresh H. Rawal* at the University of Chicago prepared a series of 1-amino-3-siloxy-1,3-butadienes. Noting that lone pair–containing heteroatom substituents on the diene render it more reactive to dienophiles and lead to improved regioselectivity in the cycloaddition reaction, they found that butadienes that contain amino and siloxy substituents are appreciably more reactive than previously made 1-methoxy 3-siloxy dienes.
In 1999, Kozmin, Jacob M. Janey, and Rawal* followed up by reporting that 1-amino 3-siloxy dienes readily undergo cycloadditions with a wide range of electron-deficient dienophiles. One such molecule became known as Rawal's diene1. Last month, Serhiy V. Ryabukhin, Dmytro M. Volochnyuk, and co-workers at four Ukrainian institutions removed the “shackles” of Rawal’s diene’s low commercial availability by reporting a kilogram-scale synthesis of the compound. They also demonstrated the advantages of the diene in multigram syntheses of 2-alkyl-2,3-dihydro-4H-pyran-4-ones, which have applications in medicinal chemistry.
Organoboron hydrides are particularly useful compounds in organic synthesis. One such molecule, pinacolborane2 (HBpin), is a stable, liquid 1,3,2-dioxaborolane derivative that is useful for hydroborating alkenes and alkynes. HBpin was first synthesized by Soviet Union chemists in the late 1960s. The first description of its hydroboration reactions came in 1992, when Charles E. Tucker, Jessica Davidson, and Paul Knochel* at the University of Michigan (Ann Arbor) reported its use for the mild, stereoselective hydroboration of functionalized alkenes and alkynes. The authors pointed out that HBpin has several advantages over another boron hydride, catecholborane3, including milder reaction conditions, greater functional group tolerance, higher regio- and stereoselectivity, and better stability of the product pinacol alkeneboronic esters.
In April, Rana B. Abdu and Courtney C. Roberts* at the University of Minnesota (Minneapolis) disclosed a more nuanced use of HBpin. They used the compound to effect a transmetallation reaction with yttrium(III) complexes that contained a tris(amido) redox-active ligand. The authors discovered that rather than the expected B–H bond cleavage, B–O bonds were broken during the reaction; and the tris(amido) ligand transferred to the boron atom. These results were actually a disappointment because the side products that were formed hindered desired C–C cross-coupling reactions.
1. CAS Reg. No. 194233-66-4; SciFinder name: 1,3-butadien-1-amine, 3-{[(1,1-dimethylethyl)dimethylsilyl]oxy}-N,N-dimethyl-, (1E)-.
2. CAS Reg. No. 25015-63-8, SciFinder name: 1,3,2-dioxaborolane, 4,4,5,5-tetramethyl-.
3. CAS Reg. No. 274-07-7.
Molecules from the Journals
MOTW briefly describes noteworthy molecules that appeared in recent ACS journal articles. See this week's edition.
This molecule was suggested by a reader. We present almost all of the molecules suggested by our readers. If you have a molecule you would like us to consider, please send us a message. And thank you for your interest in Molecule of the Week! —Ed.
Calcium carbonate
fast facts
| CAS Reg. No. | 471-34-1 |
| SciFinder name | Carbonic acid calcium salt (1:1) |
| Empirical formula | CCaO3 |
| Molar mass | 100.09 g/mol |
| Appearance | White crystals or powder |
| Melting point | 825 ºCa 1339 ºCb |
| Water solubility | 13 mg/L (25 ºC) |
a. Aragonite.
b. Calcite.
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