Generated by SassMeister.com.

SassMeister-input.scss

// ----
// Sass (v3.4.4)
// Compass (v1.0.1)
// ----

@function char-from-code($iso-char) {
  @return unquote('\"\\#{$iso-char}\"');
}

.test {
  content: char-from-code(83);
}

// further exploration of this issue
$quotedform: '\"\\\"';
$unquotedform: unquote($quotedform);

.underthehood {
  content: $quotedform;
  content: $unquotedform;
}

SassMeister-output.css

.test {
  content: "\83";
}

.underthehood {
  content: '"\\"';
  content: "\";
}