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Key Chemicals Month
This month we feature chemicals that have important applications in industry and the lab.鈥擡d.
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 鈥溾濃攁n early treatise on equilibrium and what soon after became known as Le Chatelier鈥檚 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 S枚nke 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 . When they assessed the animal鈥檚 vision, they found that the ocelli 鈥渟ee鈥� with an angular resolution of 鈮�9鈥�12潞.
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聽hazard information*
| Hazard class** | GHS code and hazard statement |
|---|---|
| Short-term (acute) aquatic hazard, category 3 | H402鈥擧armful to aquatic life |
*Most safety data sheets state 鈥渘ot a hazardous substance or mixture鈥� or similar wording.
**Globally Harmonized System (GHS) of Classification and Labeling of Chemicals. .
Molecules from the Journals
In 1997, in a search for more reactive dienes with which to conduct Diels鈥揂lder 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鈥揷ontaining 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 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 . 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 鈥渟hackles鈥� of Rawal鈥檚 diene鈥檚 low commercial availability by reporting a 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 . 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鈥揌 bond cleavage, ; 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鈥揅 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聽almost all of the molecules suggested by our readers.聽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! 鈥擡d.
Calcium carbonate聽
fast facts
| CAS Reg. No. | 471-34-1 |
| 厂肠颈贵颈苍诲别谤听苍补尘别 | Carbonic acid calcium salt (1:1) |
| Empirical formula | CCaO3 |
| Molar mass | 100.09 g/mol |
| Appearance | White crystals or powder |
| Melting point | 825 潞Ca 1339 潞Cb |
| Water solubility | 13 mg/L (25 潞C) |
a. Aragonite.
b. Calcite.
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