# Plaaben Compounds--Part I: An Overview of Their Characteristics, Detection, and Impacts
## 2 Paraben Characteristics and Applications  
Parabens are present in nature, in bacteria [13] or plants [14; 15] and fruits [16] and have been synthesized and used by industries since 1920 [17]. They are esters of p-hydroxybenzoic acid with different alkyl (methyl, ethyl, propyl, isopropyl, butyl, isobutyl, pentyl, heptyl) or aryl (benzyl, phenyl) groups [15]. Table 1 presents a summary of some properties of a wide range of parabens. The use of these types of compounds is due to their good preservation and antimicrobial properties, but also chemical stability and low production costs, which render these compounds a good option to be used by industries [1; 20]. Additionally, the low frequency of sensitization, their water solubility which is sufficient to produce solutions, inertness, the fact they do not change consistency or coloration of products and their nonperceptible odor or taste are properties which make parabens interesting compounds [20]. In parabens, an increase in alkyl chain length improves antimicrobial effectiveness, but the water solubility decreases, as can be seen in the Table 1[21]. Parabens are more efficient as preservatives against fungi than bacteria, and, regarding the action against bacteria, they are more efficient against Gram-positive than Gram-negative bacteria. Their range of effectiveness may be wider when used as a combination \begin{table}
\begin{tabular}{c c c c c c c c} \hline \hline \multirow{2}{*}{**Compound**} & **CAS** & **Molecular** & **Melting** & **Boiling** & **Solubility in Water** & **Dissociation** & **Octonal-Water** \\  & **Number** & **Formula** & **Mass/(g/mol)** & **Temperature/(°C)** & **Temperature/(°C)** & **at 25 °C/(mg/L)** & **Constant** & **Partition (Log**)** \\ \hline Methylparaben (MP) & 99-76-3 & C\({}_{\text{H}}\)\({}_{\text{O}}\)\({}_{\text{3}}\) & 152.15 & 131 \({}^{\text{h.c}}\) & 270–280 \({}^{\text{b}}\) & 5981 \({}^{\text{a}}\) & 1.96 \({}^{\text{ac}}\) \\  & & & & 275 \({}^{\text{c}}\) & 2500 \({}^{\text{c}}\) & 8.17 \({}^{\text{a,b,d}}\) & 1.66 \({}^{\text{d}}\) \\ \hline Ethylparaben (EP) & 120-47-8 & C\({}_{\text{H}}\)\({}_{\text{H}}\)\({}_{\text{O}}\)\({}_{\text{3}}\) & 166.17 & 116–118 \({}^{\text{b}}\) & 297–298 \({}^{\text{b}}\) & 1894 \({}^{\text{a}}\) & 2.47 \({}^{\text{ac}}\) \\  & & & 117 \({}^{\text{c}}\) & 297 \({}^{\text{c}}\) & 8860 \({}^{\text{a}}\) & & 2.19 \({}^{\text{d}}\) \\ \hline Propylparaben (FP) & 94-13-3 & C\({}_{\text{H}}\)\({}_{\text{2}}\)\({}_{\text{2}}\)\({}_{\text{O}}\)\({}_{\text{3}}\) & 180.20 & 96–98 \({}^{\text{b}}\) & 285.1 \({}^{\text{c}}\) & 529.3 \({}^{\text{a,b,d}}\) & 8.35 \({}^{\text{a,b,d}}\) & 3.04 \({}^{\text{a}}\) \\  & & & 97 \({}^{\text{c}}\) & 300 \({}^{\text{d}}\) & & 2.71 \({}^{\text{d}}\) \\ \hline Butylparaben (BuP) & 94-26-8 & C\({}_{\text{H}}\)\({}_{\text{H}}\)\({}_{\text{4}}\)\({}_{\text{O}}\)\({}_{\text{3}}\) & 194.23 & 68–69 \({}^{\text{b}}\) & 300.3 \({}^{\text{c}}\) & 159 \({}^{\text{a}}\) & 3.57 \({}^{\text{ac}}\) \\  & & & & 68.5 \({}^{\text{c}}\) & 150 \({}^{\text{a}}\) & & 3.24 \({}^{\text{d}}\) \\ \hline Benzylparaben (BeP) & 94-18-8 & C\({}_{\text{H}}\)\({}_{\text{2}}\)\({}_{\text{O}}\)\({}_{\text{3}}\) & 228.24 & 110 \({}^{\text{c}}\) & 170 & 107.80 \({}^{\text{a}}\) & 8.18 \({}^{\text{a}}\) & 3.56 \({}^{\text{a}}\) \\  & & & & & 50 \({}^{\text{d}}\) & 8.50 \({}^{\text{c}}\) & 3.27 \({}^{\text{c}}\) \\ \hline Pentylparaben (PeP) & 6521-29-5 & C\({}_{\text{H}}\)\({}_{\text{4}}\)\({}_{\text{O}}\)\({}_{\text{3}}\) & 208.25 & n.a & n.a & 62.50 \({}^{\text{a}}\) & 8.50 \({}^{\text{a}}\) & 3.96 \({}^{\text{a}}\) \\ \hline Phenylparaben (PhP) & 17696-62-7 & C\({}_{\text{H}}\)\({}_{\text{4}}\)\({}_{\text{O}}\)\({}_{\text{3}}\) & 214.21 & n.a & n.a & 253 \({}^{\text{a}}\) & 8.40 \({}^{\text{a}}\) & 3.21 \({}^{\text{a}}\) \\ \hline \hline \end{tabular}  
\({}^{\text{a,--[18]}}\); \({}^{\text{b,--[19]}}\); \({}^{\text{c}}\)\({}^{\text{--[17]}}\); \({}^{\text{d}}\)\({}^{\text{--[20]}}\); n.a.—not available.  
\end{table} 
Table 1: Properties of parabens. of different parabens [21].